I don't know why Diesel's monosyllabic Riddick makes anti-heroism in this cheesey  Lord-of-the-Rings- goes-to-space universe so compelling - but he really does.  Pitch Black's monsters had a nice retro- Alien reference thanks to Peter Chung's designs; but PB  mingled Aliens' monsters-are-out-to-get-us with a second theme of the-planet-is-out-to-get-us.  The character development was also good - the