Anyone knows ... how they differ from the actual OD&D itself?
I agree. Another thing that makes me wonder is all the errata/new editions they have for such a theoretically simple game, too.That's one of the things that bothered me about Castles & Crusades. They go to the trouble of making a "SIEGE Engine" (which is just an inverted d20 system, but whatever) to unify the mechanics, but they leave the weird class imbalances in the system out of some bizarre fealty to "old school feel." I mean, if you aren't going to make it better, why bother?
That's one of the things that bothered me about Castles & Crusades. They go to the trouble of making a "SIEGE Engine" (which is just an inverted d20 system, but whatever) to unify the mechanics, but they leave the weird class imbalances in the system out of some bizarre fealty to "old school feel." I mean, if you aren't going to make it better, why bother?
Quite simply, Davis made the game he wanted to play. He took a lot of input from the other trolls and us “playtesters”, but it was pretty clear that it was going to be whatever he wanted it to be. The only limitations were that it be legal and that Gary didn’t object to anything. (And Gary gladly just provided his own changes in the CZ stuff for anything he didn’t like.) Anything in there isn’t due to bizarre fealty. It’s there because Davis wanted it and didn’t feel it was weird.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.