Yes, those Halo3 short movies are great and one can see much of his "directing style" that went into District 9. Speaking of each, the original short movie (Alive In Joburg) has some nice combat scenes, specially the first one (SWAT? against alien in mech, if i remember correctly).
I had some hopes for Avatar, but it seems to be the "old" love story wrapped in some sci-fi trappings, with lots of eye candy and not much more :\