Hmm... well reguarding the robot's expression it can change via color and level of light emitted from his eyes. Also his stance will reflect his attitude combined with his eye-peice. But I'm not stuck on any ideas, it is just one of many things to try.

Ideas for features I'd like to consider taking from: Mega-Man(now, it was very much an anime-type cartoonish theme, with big bright blinking eyes and all, but some of the body designs and features were pretty darn cool, esp. when you got to the later additions at the end.), I, Robot yes I know you don't like them overall, but I'm refering to just the NX-5 models' idea of the sholders, knees, etc... at least how I remember them anyway...

The Matrix has another inspiring set of features for robotics. I'm not talking about the squids and the funky screensavers, but more the materials used and such.