Gotta be a solid 8 from me - a lengthy campaign (the likes or which is almost unheard of in fps's these days), stunning visuals and solid gameplay.
There are some epic moments in the game, and for me it had a real War Of The Worlds feel, which was great.
The gunplay throughout is excellent, and you have a great deal of freedom of movement - big jumps, climbing abilities, sliding. Somewhere just shy of what's possible in Mirror's Edge and what seems to be being done with Brink.
The alien adversaries are great fun to fight - as well as genuinely challenging (they're fast and smart). There's also a very solid upgrade system for the Nanosuit (read: you) and the weapons.
The only things marking it down, are the early couple hours of the campaign are a little slow (it's a 10ish hour job), and fighting the armed troops isn't terribly exciting (the aliens is where it's at).
Also, the story is pretty tough to follow in places if you haven't played the first (which I haven't).
Online, there's been some issues with net code. To be honest, I've not played it online if a few weeks so I don't know if these have been resolved yet - supposedly patches are being/have been put in place.
The multi still has the same freedom of movement and great graphics. Level design is very good and there's a fair amount of customisation. The energy of your suit is used for almost everything you do (bar walking and pulling the trigger), so there's a real emphasis on judacious use of your powers and pulling the right tricks at the right time. This lends it a nice tactical edge, which can be very satisfying.
I thoroughly enjoyed it - I will certainly play through the single player again, and I fully intend to go back to the multi as well now that I've got a bit more time on my hands (had a busy few weeks).