I agree, that a lot of it seems rushed at times, but I think this will wear of with further viewings. I wouldn't have no problem with it going on longer, though. 
The sound-design (and the music) is really remarkable. I love the scene where Champion and Mme. Souza are eating while their dog is waitinbg to get served. I think it's something like five minutes of observation and perfect sound. 

I haven't seen anything else by Chomet, but would like to see La Vieille Dame et les Pigeons. Hope he stays true to himself in the future, as the interview I saw of him makes him appear like a true artist. Hopefully he'll evolve in a positive way and get the opportunity to make even better films in the future. 

Also worth mentioning is the fact that he "Belleville Rendez-Vous" doesn't use the usual pop-culture references to entertain the older audience but has something genuine to say about our society. 
This doesn't necessary make it superior to films like "Finding Nemo" or the better Disney's, but it's far more adult. 
I'd maybe even put him on a level with Miyazaki, because of the ambiguity of his "message" and his original style, but we'll have to see if that will really turn out this way with subsequent works.