Hmmmm i would'nt be so quick to say that the Ichi manga is better than the movie, but I am really enjoying MPD, the depiction of the murders is shockingly gruesome and it does get imcomprehensibly violent later on. The plot is very complex at times it can get too confusing but thanks to some skilful exposition you can always just about tell what's going on. If you get the chance check this out it's a very refreshing and original manga...........well worth the read.
It's quite hard to summarise, It concerns a detective with multiple personalities and a dark past who solves gruesome murders for a special agency outside of the police. Imagine Seven meets Ichi the killer and you get a good idea of what to expect.
I'm a big Miike fan, but have held off buying the R2 versions of MPD i'm waiting for the R1 editions which will hopefully be unrated.
I think the manga is unlicensed but i'm sure there are plenty of scanlations out there.