Expect more RPG elements this time around -- if still not on par with Mass Effect 1 -- with beefier skill trees and more evolution of powers. You can also expect more weapon modification, though, again, likely not as much as we saw in ME1. All weapons will be usable by all classes, though each class (except for the solider) will be limited to a certain number of weapons that can be equipped for a mission.
As far as Mass Effect 3's plot ... well, suffice it to say that Shepard is on Earth due to the events of the "Arrival" DLC. But that's all we'll spill. As for returning characters -- you really don't want to know, do you? ... You sure? ... OK, fine. For now, we know Liara and Garrus (if he survived) will be playable. Favorites like Wrex and Mordin (again, if they're alive) will also make appearances, though whether they'll be full-fledged teammates is unknown.
Sorry, but that's all you're getting from us. You can check out the new issue of Game Informer if you want to spoil more for yourself, but we certainly won't be party to it.