It is often said that Castles & Crusades is the Rosetta Stone of Old School Gaming. It certainly is that, but there is a lot more going on here than just that. Castles & Crusades is very much a stripped down version of the basic 3.x SRD. As such there are lot of concepts that are modern including a one-roll mechanic for all sorts of situations. Though if that were all then there would be nothing separating this from say True20 or other "lite" d20 iterations. Castles & Crusades plays like good old fashioned D&D. The aesthetic here is 1st Ed. AD&D, with the simplicity of Basic era D&D. The concept is noble and one we see in many of the retro-clones. But where the clones attempt to use the OGL to make an older version of the rules, Castles & Crusades makes it's own rules and instead goes for the feel or nature of the game. So while you will see Thieve's abilities represented by percentage rolls in Basic Fantasy or OSRIC and as a skill in 3.x in C&C it will be a Dexterity check. Simple, elegant and easy. The Ability check, whether your abilities are Prime or Secondary, are a key element of C&C.
The Players Handbook is the first book you need for Castles & Crusades. At 140+ pages it is all about getting your character up and going. The abilities here are the same six you have always used and they are even generated by rolling 3d6 and assigning. If you have a different method that you liked back in the day OR if you have adopted some point by system from a new version I see no reason why it would not work here. I am a fan of 4d6, drop the lowest myself. The ability score modifications are a bit different than new OGL games, but are in fact much closer to older games. Bottom line is just pay attention to how many pluses that 18 gives you if you are used to playing newer games.
Next you will choose a class based on your abilities. Each class has a prime ability; one that is most associated with it. So fighters have strength, clerics wisdom, wizards intelligence and so on. Speaking of classes, all the "classics" are here and some new ones. So you have Assassins, Barbarians, Bards, Clerics, Druids, Fighters, Illusionists, Knights, Monks, Paladins, Rangers, Rogues and Wizards. There are some minor tweaks that make them different from other versions of the same class in another game, but nothing that made me scream "That's not right!" in fact in most cases I was more inclined to agree with what they did. For example I like the Barbarian for the first time ever. Each class has some special abilities and skills. In C&C it is assumed that if a character wants to do something that instead of a skill roll an ability check is made. There is Target Number, 12 for Primes (something you are good at) or an 18 for Secondary. You add your mods, any class or race based modifications and there you go. Simple. Skills are no longer of a list of things you can or can't do, but now potential to do or at least try anything. This is something we did back in the old days, but the newer twist here is that this is just the same as any d20 based roll. Be it skills or attack. So Rangers and Barbarians are good at tracking, wizards at arcane lore and so on. makes things pretty easy. So improvement over 3.x games, no tracking skill points. I have to add, that there is such a cool old-school vibe here that it is just like reading a book from the early 80s. Only with far better layout and art. As another aside, the art is fantastic. I love my old school games and wizards in pointy hats and all, but the wizard in C&C looks AWESOME. I would not mess with that guy, I don't care if he looks like a farmer or not.
Races are up next and all the usual suspects are here. Races and Classes are built in such away that customization is REALLY easy. If I wanted to play a Goblin here I bet I could rather easy. Every race gets two Prime stats. Typically you want one of these to correspond with your class. Humans get three allowing for their flexibility. All other races also get modifiers to abilities and/or special traits. While the modularity of 3.x is obvious, the feel is still more 1st ed.
We end character creation on completing the character with persona, gods and alignment. Up next are some lists of equipment and rules on encumbrance. The rules are some of the easiest encumbrance rules I have seen. So far so good? Well we have by this point gotten through roughly a third of the book. Not too bad for 50 pages.
Magic and Spells take up the remaining bulk (65 pages) of the book. Not a surprise given four spell casting classes. Spells are listed alphabetically and range from 0-level cantrips to 9th level spells for each of the four classes. That is a major break from their old-school roots when only wizards had access to 9th level spells. The spell format itself is also closer to that of 3.x, though no XP penalties that I could see. The nest 20 or so pages deal with the Castle Keep (GM) of the game. This includes all sorts of advice on how to handle conflict, award XP and even how to set up an adventuring party. Good advice all around to be honest and enough to keep most groups going for a long time. There is also an appendix on multi-classing as an optional rule. I have not tried it yet, but it looks solid. Not as elegant as what you see in 3.x, but better than what we had in 1st or 2nd ed.
The Players Handbook is all most players will ever need and even some Castle Keepers.