If you want to tweak your C&C game, look no further than this book. Basically the Castle Keepers Guide takes a toolkit approach to modifying the Siege Engine. Much of the optional rules re-introduce elements of the full 3.x SRD, but the real beauty of the book for me is in the analysis of the game engine. Highly recommended for anyone interested in spicing up their C&C game.
[4 of 5 Stars!]