HeroClix Alpha strips the Heroclix system down to its essentials, for an overall mixed result. It gets rid of the concept of "pushing" actions, which simplifies things for teaching purposes. although at some cost in tactical subtlety.
One welcome change I'd like to see ported over to the mainstream rules are the revised victory conditions. In regular tournament HeroClix battles are won by points scored, with each KO'd figure worth its build points. In HeroClix Alpha victory is achieved by the first player to KO five opposing characters.
One of the things this does is restore bystander tokens to their secondary status. I've noticed that many tournament players include a few bystander tokens and use them aggressively to tie up enemy figures, block lines of fire and otherwise take suicidal risks. While valid game tactics, it really seems out of sorts with the theme. I mean, sticking Martha Kent in front of Superman is just wrong. But hey, if Franklin Richards gets blasted by Kobra, so what? He's only worth a few points.
Under the Alpha rules, in contrast, bystander tokens are a source of weakness. A KO is a KO, and it's obviously a lot easier to pick off a one-step Joe Chill than a 10-step Batman. Bystander tokens, if used at all, will probably be kept in safe spots, which seems a much more appropriate place for Mary Jane Watson.