Some thoughts on what I've played for (almost finished recruiting kims for my mission, I think). The universal ammo pickup system/combat system is quite cool, means you're free to (and have to) use pretty much everything you've got, rather than stacking it all in assault rifle, which is what you did in the first one if you wanted to knock seven shades of shit out of everyone.
It's nice to see familiar environments in it (Normandy, Citadel), although I'd like to figure out how to see the whole Presidium, rather than just the Councillor's balcony bit...
The recruitable characters are very cool, but not so much when you meet them... The Convict I was hoping would be a properly sick fucker who you'd constantly need to keep an eye on, and the Krogan warlord guy doesn't seem anywhere near as interesting as Wrex (my favourite character from the first game). The Archangel likewise, I had a feeling it would be Garrus. He's received a bit of haunted backstory, but he's essentially a standard tightarse extreme justice type.