I've seen both movies recently. I enjoyed District 9. I thought the social commentary was very prominent but stopped just short of annoying me. I don't like it when movies beat me over the head with their message (Lions and Lambs, etc.)
I LOVED Inglourious Basterds. I was also expecting more "Brad Pitt talks funny and kills Nazis in interesting ways" but in hindsight, I'm glad that isn't the route Tarantino went. I think that it wold have been entertaining, but would've gotten repetitive (ala Kill Bill). As others have mentioned, Chris Waltz was excellent as Col. Landa (be glad this guy doesn't work at Fairchild). I thought Brad Pitt did a good job of keeping his character over the top but not crossing into the absurd. I'm an admitted Tarantino fan But I really enjoyed this movie and think its probably his best work since Pulp Fiction.
EDIT: Another thing I really liked about this movie and failed to mention is the soundtrack. Tarantino does an amazing job of selecting music for his movies and Basterds is no exception. I particularly liked the Ennio Morricone piece he uses in the opening scene.
And Diane Kruger is smokin'