My big complaint with Resistance is that the game feels kind of sterile. Whereas the world of CoD4 feels really alive, and able to be blown apart and manipulated, Resistance has that perfectly still museum feel, for the most part. The glass in the game is fuck awesome, though.
I enjoyed Resistance. It accomplished its task, providing a good launch title, but I've always kind of felt that it would be the sequel that proved whether the game was a viable series, or just a good launch title.
The multiplayer impressed me. They really got that working well, at launch, even.