I also thought his books tended to have weak endings. It seems to me that he likes to keep the reader guessing, so he'll introduce characters and entire plot lines that in the end are irrelevant and since they never get tied into the ending they are just loose ends left hanging out there. Some of it can be considered world-building, which I do have to say he's pretty good at, but other times it's just a chapter of gratuitous gore with characters that you never see again and where everything that happened doesn't advance the plot or even matter.
I have to agree with the pacing too, particular in Consider Phlebas where the final act
just seemed to drag on and on.spoiler
with the underground train system