I can't emphasize how much C&C encourages you to tinker with it -- for example, I have a C&C game with hybrid weapon mastery from Basic D&D and Arcana Unearthed, segments and the helmet rule from 1e, the thief acrobat character class from Arcana Unearthed, Specialty Priests from 2e, the Mind Witch character class from Monte Cook's Arcana Evolved system, the Gem Witch character class from the Diamond Throne website, the Crimson Mist feat and a couple of other things for barbarian characters from the Conan system, death at variable negative hp from some online poster, my own grappling and overrunning system which is much simpler than the 3e system, the harsher d20 Modern massive damage threshhold, the concept of damage with exploding dice under certain circumstances from another game, and about 20 generally very simple feats from various sources (including some 3e feats and the Enworld 1e Feats pdf). I've assembled all of my favorite spells from all of the systems that I just mentioned including forty or fifty from Monte Cook's Arcana Evolved with different spells open to priests of various deities, the illusionist class, and the two witch classes. This whole massive system of choices, etc. is at most one-third as complex as 3e. The point is that C&C is such a simple engine that you may decide that you want to add x or y to that.