I prefer Hero Factory aesthetics to Bionicle. I really like the solid, refined, angular designs over the organic bionicle parts which from time to time would be too busy and create results that were cluitered to the eye.
While Hero Factory is designed to be simpler it also makes characters look more appealing and overall more attractive. I do believe it is time for some specialized parts for the sake of variety. We have been using the same feet since the 2.0 series, save from Bionicle claw feet for some of the enemies and the odd Ben10 feet. We got Stormer XL feet but they are not particularly nice or versitile. I'd like to see more feet variety. Perhaps a new design altogether. Also, I think it's due time to get proper back pieces designed. You can only be so creative with feet and multi tool pieces used for backs. After a while MOCs end up looking too simiral with so few options.
I think Lego is in the right track with the ball and shell system. They've come up with a simple and elegant system that has proven very versitile even in the face of its own limitations. I'd like to see more variety in textured pieces and specialized pieces that can be attached to existing shell like the knee pads and shoulder pads offered in the Breakout sets. In a sense I'd like variety.