New enemies called the Collectors and new Husks; they're creepy as hell.
http://www.joystiq.com/2009/11/05/the-coll...-mass-effect-2/9 Mins of Omega action with cameo by one Badass Garrus.
http://www.joystiq.com/2009/11/06/nine-str...ect-2-gameplay/Look like there's an Asari running the show on Omega. Also, remember how we have that Geth faction? Guess what turned out to be the case. Some creepily awesome lines there.
Legion: "We do not experience fear, but we understand how it affects you."
Thing's got an awesome voice effect.
Collectors are some sort of insect hivemind (of course) with BEAM WEAPONS! Enthusiasm aside, the flying aspect seems mildly interesting. Plus they have a super-bug version.
Husks have been given some work with exploding zombie types that are on fire (abominations), heavy weapon zombies (scions), and nightmare-fuel flying zombie of doom (batorian, which sounds like a batarian).
We get a good look at the YMIR Mech (Shepard tears through it like a hot knife through butter).

It also show three health types: shields, armour and health for gameplay.
Speaking of gameplay, ammo returns in the form of heatsinks. Fire your shots, eject the heatsink and slap in a new one. Kinda makes sense from the engineering point of view because heat takes forever to dissipate without active cooling.
Final word, Garrus looks like he's been on a bender but still kicks ass with a sniper rifle.