Some more info is coming out from the OXM review and CES.
There are 6 different heavy weapons in the game, but only 4 of which are explicitly named: missile launcher, grenade launcher, a particle beam, and the Avalanche, which apparently is essentially a freeze gun. These replace grenades from the first game, as previously mentioned.
Matching armor provides set bonuses, like Dragon Age. You can customize your party members' armor (including cosmetics) and weapon loadouts as well as your own.
The really obnoxious camera shake when you look down the scope of the sniper rifle is gone, so it's a much more viable weapon this time. Picking up heatsinks from enemies or the environment will add ammo to all weapons, but ammo is not interchangeable between weapons.
The review doesn't specifically talk about who is/isn't romanceable, but does mention specifically that you can bang at least some of the aliens, if that's your thing.
Enemies now have different AI based on species, e.g. Krogan opponents will be much more aggressive than humans. Squad mates will also have their own individual AI patterns, provided that you aren't directing them. Both your squad mates and enemies are much more talkative in combat as well. Enemies will also talk to directly to you: for example, one guy heard a krogan insult him for using the cloak ability, as well as telling him to 'use a man's gun' after shooting the krogan with a pistol.
This part's a little vague, but apparently the bonus for importing a high level character is just credits (and maybe some bonus experience? I'm getting conflicting info here). There are supposedly three tiers of bonuses for levels 35, 50, and 60. However, other stuff can get you bonuses at the beginning too. If you were a dumbass like me and tracked down all those minerals, you'll get more at the start of ME2, which will get you a head start on the research projects which determine upgrades for your squad/the Normandy.
On the 360, the bumpers and the Y button can be used as hotkeys, for either Shepard or your squad members. Left and Right on the D-pad each control an individual squad mate, and can either be used to position them separately or as additional hotkeys. Up is to direct them both at once, and Down is to pull them back. I'm guessing that the power wheel is now used with the Back button, since there are no more grenades.
Supposedly, nearly every decision in the first game will have at least some impact on the second game. People you saved on various side missions will show up, as will the batarian terrorist from BDtS if you let him go.
Unexplored planets are now scanned remotely, and you'll only send down a landing party at all if you find an anomaly. Examples given were merc outposts, mining facilities, and missile bunkers.
The framerate and pop-in problems from the first game are fixed, according to hands-on accounts from the CES floor. Cover is much better and closer to Gears style now, including the ability to vault over low cover.
Charm and Intimidate are no longer separate skills. Instead, your class-specific skills (Combat Mastery for Soldiers, Biotics Mastery for Adepts, etc.) will give you passive persuasion bonuses as you rank them up, and the extra dialogue options will be determined directly by your Paragon/Renegade score. Those still go up independently of each other, and apparently there is enough content in the game to max both bars in a single playthrough.
That's about all I got out of the past few days in terms of ME2 info. Anybody decide on who their squad will be in the second game yet? Since I'm playing a Vanguard my first time through, I'm going to want to roll with a sniper so I'm not charging into huge crowds constantly, so I think I'm gonna need either Garrus or Thane. The third person will probably depend on what I still need (if I take Thane over Garrus I'll need at least some tech skills on my third member) and/or whose jib I find sufficiently cutting.