The anime is consisted of two seasons : the first one is 24 episodes while the second is 12 episodes. The first season's first 18 episodes closely follows the manga with few differences, while the last six episodes and the entire second season, while following the manga, has major differences.
I don't know about Bleach, but the anime adds comedy and some filler scenes to the manga story, while still following it. Also, they totally screwed up episode 10.5's adaptation.
I still prefer the original, though. Get ready for a lot of religious references while you are at it, too.
