OSRIC is ostensibly marketed as a resource for writers who wish to legally write supplements for AD&D. However, considering the effort put into organising it, with a table of contents, index and appendices, and that it comes out to 128 pages with a full art cover page makes it look much more like a real rulebook.
I have the AD&D 2nd Edition Revised PHB, DMG and MM (among a ton of other supplements). Given that OSRIC is supposed to do AD&D 1st Edition I can't compare exactly whether it covers everything, but it is definitely complete enough and covers the rules fine.
It is split up into 3 chapters. Chapter 1 is character creation, chapter 2 is how to play and chapter 3 is spells. Chapters 1 and 3 are PHB chapters, and chapter 2 would normally be in the DMG. What it lacks from the DMG is extensive magic item tables, but aside from that all the useful advice is still in OSRIC (another indication that it was intended as more than just a legal workraround for supplement writers).
The tables are complex, and I'm guessing this has to do with THAC0 being non existent and a "To Hit Armor Class ____" table has been put in instead. It can't be easily extrapolated, because the next 5 AC levels from when a 20 would be required to hit are also all 20, after which it increases by 1. This is close to the "natural 20 always hits" rule, but after a certain point it becomes too much.
Races all appear to be correct for the most part. The only thing I find incredibly strange is that every race except half-orc has thief as their class where they don't have a level limit. With the exception of halfling and perhaps half-elf, this makes absolutely no sense. What makes even less sense is it has been out since 2006, and given that it's a PDF it wouldn't take that much time to fix. If this was actually how the rules were handled in AD&D 1st Edition I can't figure out why. While the saving throw tables are completely arbirtrary, so other aspects of the game don't necessarily make that much sense - this seems counter intuitive and I would automatically house rule (essentially just employing errata that hasn't been published) that dwarves would trade the fighter and thief levels, gnomes illusionist and thief, elves magic user and thief, and half-elves ranger and thief.
Another part with level caps which I don't believe to be an error, but is a flaw, is the level caps are ridiculously low. A halfling fighter tops out at level 4. This makes it almost mandatory for demi-humans to multiclass if they want any class other than the one they have unlimited in (from this point onwards I'm assuming my "errata" for the actual rules), and multi-class with their unlimited class so they can get the flavour of the class they want, but are still able to advance past that point with the rest of the party. I would also be tempted to house rule an extra 5 levels onto every level cap, except where it would put assassin or druid over 15 or 14 respectively - due to the classes capping there in the rules.
The multiclassing section doesn't clarify what happens if you reach your level cap in one class but don't in another class. Given that it's AD&D and doesn't require a rule for everything unlike d20, I would just assume that after that point the character would advance normally, without splitting hp or xp (and in the case of 3 class multi-classes going to just 2, then 1). Dual-class doesn't have any mention of a maximum of 4 classes as is stated in 2nd edition, but the name dual-class pretty clearly suggests that it would only be 2 classes. The requirements would also prevent anyone from getting more than 2 classes given how ability scores are rolled.
Magic users, and illusionists are seriously hobbled at lower levels. With 1d4 hp, and no house rule that every character starts with max hp for 1st level, a magic user or illusionist has no choice but to take a weapon proficiency in darts and spend most of the time until they reach level 5 keeping back and throwing darts at their enemies. Once magic users pass level 9 they start really becoming as powerful as they should be, and with advancement topping out at level 29, and their extensive spell lists at the higher levels they do end up being the most powerful. Illusionists seem to just be weaker than magic users at all levels, although the nature of illusion spells allows for them to be much more creative with their available spells at lower levels.
The rest of the classes are much more solid at lower levels. A fighter quickly drops off after 9th level though, aside from increasing to hit rolls, saving throws and a small increase in hp. Thieves start dropping off after 13th level. Rangers and paladins don't really drop off, they just change focus around 10th level as they both begin to acquire spells.
Clerics and druids follow a different pattern, druids change several times from levels 1 to 14 and there's no clear area where they begin dropping off or having a major change. Clerics are much the same way but they top out with their spells at level 29, and the only drop they experience is hit point advancement after level 9.
Assassins are also a bit different, being along with rangers and clerics the most top heavy class. Rangers get 2d8 starting hp, which simply due to the bell curve is a huge advantage over every other class, including fighters and paladins. Clerics have the ability to cast spells, bonus spells for high wisdom, the ability to use armour and powerful weapons and the ability to turn undead. Assassins also have a full range of abilities, and the most notable being assassination. A first level assassin has a 5% chance of instantly killing an 18th level character in one hit. Obviously it's only a 5% chance, but that's still really noticeable. Considering that most opponents of a party won't be more than a level or two above the assassin, the chance will likely not be lower than 40% most of the time.
Game balance is obviously not a huge concern, and the combination of top heavy and bottom heavy classes, with level caps for demi-humans will probably result in chosing classes based on whether the campaign is expected to be short-term or long-term. A long-term campaign will encourage more humans, and actually have some people playing magic users or illusionists. A short term campaign would probably not have anyone playing a magic-user or an illusionist as they wouldn't get much play time in the beginning. Even rolling low scores on everything except intelligence probably wouldn't encourage playing a magic user in a short term campaign for the first 3 levels a fighter with strength 9 would get more play time than a magic user with intelligence 18. Incidentally, this has only been marginally fixed in d20. The most sense would probably be to hire an NPC magic user when one is expected to be necessary.
The equipment list is better than I remember from 2nd Edition. Particularly with the case of wizards who maxed out at 50GP if they were lucky and spellbooks cost 40GP. With magic users having 20GP-80GP they can usually buy a spell book for 25GP and still have something left over, but with a bad roll, it's not good that they don't have a scroll option for 10GP so a magic user can at least have a spell to start with. The other sollution is for GMs to house rule that all magic users start with a spell book.
One complaint I have is that secondary skills are missing. While non weapon proficiencies just add unnecessary time to character creation, the secondary skills table in the 2nd Edition PHB would have been welcome here. Rolling quickly to get a non-class career for the character helps flesh out character depth and give some extra skills that would normally not be easily available. I don't know if they had them in 1st Edition, so that might explain their absence. I would like a non-PDF version of OSRIC that I could use to fix the level caps and insert Secondary Skills into for use in play.
Chapter 2 covers the most important aspects of playing that would have been in the DMG. What I really like is the scaled xp rules that they dragged in from d20, although it's more just a suggestion than an official rule, the idea that a level 10 fighter shouldn't gain xp for killing an Orc is good. Of course it probably wouldn't make a huge difference considering the xp required to level when you're 10th level, but the xp creation tables for monsters is welcome. It also makes it easy to add character classes to monsters and increase the xp for them accordingly. The other useful aspect is taking monster descriptions from generic RPG supplements that are designed to be used with any system. I think this would have been harder with the system they had in the DMG with 2nd Edition than with the system.
The rest of the chapter basically covers rules that relate to dungeon crawls. My 2nd Edition DMG coveres a bunch of other terrain types, although it isn't that hard to house rule different terrains. It's also a bit strange that wilderness isn't covered considering druids and rangers have specific abilities for the wilderness.
The spells in chapter 3 are about what you would expect a chapter on spells to be. Overall it's well done except contact other planes has a table that starts on the end of 1 page and continues onto the next. Entering some blank space in there would be the other change I would make if I had a non-PDF version of OSRIC. The other thing that's a bit annoying is that it followed the 3rd edition standard of spells in alphabetical order. Having spells in order by level is far more useful, especially when it comes to initially creating characters and chosing spells for magic users and illusionists. Looking at the spell lists and then flipping to the actual spell is a bit of a pain. On the flip side, since the spells are in alphabetical order there's no need for a spell index, which combined with organising the spells in order of level would have probably extended the length of the book. Since it's a PDF this really isn't a problem though, I almost get the feeling they confined it to 128 pages to fit the feel of old AD&D products that always had 32, 64, 128 or 160 pages. Considering it's a rulebook, adding in extra pictures, more spacing and setting it to 160 pages would have made more sense though.
The appendixes basically just had all the tables in one place - very important considering how much reliance on tables there is. One problem is the thief ability tables for high dex just have Etc for 19+, whereas the original table has additional +5% or +3% per point. Given that it's logical to assume +5% for all of them it's a bit of a problem how it was done.
Overall I like it. The fact that it's a PDF makes it more handy in some ways than a printed book. Having a single perfect bound book would be possible with it, but I would print each chapter seperately, and would probably split up the different spell types as well.
My biggest complaint is that it's only in PDF form, which is a huge pain to edit compared to RTF form, which is easier to take and convert into a PDF for personal use. Given the ostensible purpose of OSRIC, it would also make more sense to just have it as an RTF file and nothing as a PDF.
Style wise I give it a 4, there's the occasional picture thrown in, although more would be welcome. The fact that one race just runs into the other and one class into the other is what keeps it from getting a 5. It gives all the information it needs to, it's easy to read for the most part, but it could do with some organisational improvements - it's digital, more white space won't take up much extra data or bandwidth, and printing costs are very low.
For substance, it's supposed to recreate AD&D 1st edition, so it's hard to criticise it for missing out information that AD&D1E might not have had. Still, it could have done with some optional additions to bump it from a 4 to a 5. Chapter 2 was particularly sparse for a DMG, but since it appears to be a PHB it actually counts for adding to the substance.
If I was rating it as a DMG, I would give it a style of 3 and a substance of 2.
