"Riddick" was a very well made movie and entertaining, but I consider it the weakest of the three films because it was basically a remake of Pitch Black. Only the monsters were substantially lamer this time around. I really enjoy the Riddick character, definitely Vin Diesel's most entertaining character.
I guess I'm one of the few who really liked "Chronicles of Riddick" and was looking forward to a proper sequel dealing with the Underverse.
I also found the structure of the film to be quite bizarre. Act One is almost a silent movie with Riddick playing castaway with a demon dog instead of a volleyball. Act Two doesn't really show Riddick just the mercs' reactions to him. Then Act Three is Pitch Black Redux.
And what was up with seeing Starbuck's boobs for two seconds? I can't believe she agreed to that.