Boring show, terrible animation, lack of good facial expressions and emotions. The transformations were half-assed at best, proven when they tried to re-animate ben's original aliens for the show - 7ALU (original Heatblast) vs. 2Honq6AJIw (Alien Force Heatblast). There's an obviously enormous drop in quality. Additionally, all the new aliens are crap.
Except Rath. I have to say, he honestly amused me a lot, and being voiced by John Dimaggio (Bender, Futurama) really helped with that. Other than him, though, LAME.
One other thing, though: I like Omniverse. I've heard a lot of negative feedback (heh heh - Feedback) about it, but it's at least a crapload better than Alien Force. The art style really helps, even with Ben's new pupil-less, soulless eyes. Plus they made Eatle cool.