C&S is the bees knees. It delivers everything it promises, just in a package that made more sense in 1977 than it does to a modern eye. I recommend 1st edition, both because it is often most interesting to read an author's first take on a creative idea, when the inspiration is still fresh, and because it is actually the best single volume presentation of the game. 2nd edition is more or less the same material re-organized and re presented (but also redacted of some cool material). 3rd edition did nothing to improve the brand. 4th edition heads off in directions that can only be described as heavily system-focused. Basically, they decided to 'fix' all the arbitrary mechanics in the original game, and ended up climbing up their own asses in an effort to present the most detailed and realistic possible presentation of skills, armor, etc. for a medieval game. The end result is a very solid game and better, just in a design sense, than anything that came before. But at a heavy cost: there is basically no anima left in the books because all the cool stuff that made C&S unique were left on the cutting room floor.
I could go on and on; I played and ran a ton of this game, own a complete set of all 1st edition materials in beautifully preserved copies (as well as later editions), and I often go to these books for ideas in my own game design projects. I don't have the time or inclination to spew all my thoughts into one post, but ask away if you are interested about anything in particular!