His drumming for them doesn't blow me away either, just he really sticks out to me in White Mist for some reason.
Gavin's a great drummer, but he really reuses a lot of the same tricks; ie use of splashes, his custom chimes, tom flams and such. We've kind of heard it all from him. Porcupine Tree is and probably will be his greatest work. His playing on Anesthetize (the track, and studio version only--can't stand the live version of it for some reason) is so damn good to me.
So I guess to me, TPT is just kinda Gavin by Numbers, nothing new or different, just his identifiable sound. I know it's him playing. It's not a knock on him, just what I hear.