As for why you'd want to choose one class over another, the trailer doesn't really specify. It's focused more on pretty moving pictures than a detailed breakdown, presumably to make you want to play and find out for yourself.
Fortunately, that won't cost anything ...yet. A free four-map multiplayer beta of EA LA's strategy sequel is currently open to all, with the full game slated to hit March 16.
It seems like beating a dead horse. Did anyone love the beta?
I'm not sure how much of the horse is left after the last few releases.
Problem is not so much that it's going to be a bad game, but why exactly would I want to buy it? Usually that's quite easy to answer for a series I am fond of, but here I just see no reason to get excited.
And class-based gameplay is just the latest fashion for games, whether or not it fits in.