Err ... there's only two Castle Zagyg supplements now (The Upper Works and The Dungeons). Still, buy away, and the more the merrier. How's OSRIC going? {edit: obviously, replying to P&P two posts up}
At any rate, on the topic of character customization, I think one often overlooked component of C&C is the "Rewards" section of the Monsters & Treasures book, which suggests various ways in which different character classes can be rewarded for their deeds, specific to their classes and roles. C&C characters are differentiated "in play" as opposed to "in design" - thus the differentiation through a combination of the use of Primes, class skills, known "skills" as defined through character background and play, and rewards earned through play. Obviously, there are many people who enjoy a "customized build" system (d20, GURPS before that, etc.) versus a "customization through play" system, but it's great to have C&C as a banner-bearer for the older style of play.
Cheers