I'm nearing the end of the game now, my first run through.
Pros:
This is pure Deus Ex in terms of style of story. Complicated, but in a fun, nearly campy way - the multiple conspiracies and even the high brow philosophy is pure entertainment, not annoying dribble.
Immersion is quite high, and that "intimate" quality to the levels Spector spoke of is definately in full effect.
Production values for the voices, artwork, etc. seem quite high - and there's no skimping on work to allow for multiple outcomes to nearly any scenario, no matter how remote it might seem ( killing a character early in the game, etc )
Some of the tie-ins and inside jokes to the first game are glorious.
Combat is usually highly fun, especially later on in the game when you are properly bio-modded up and can seriously whup ass.
Cons:
Unified ammo can drain all your weapons at once.
Lack of skill tree lowers character development and flexibility.
Performance hog.
Overall, it's a good to great game. I argue heavily against people who say it's too short. If you beat this game in 10 hours, as I've heard some reviewers quote, you aren't seeing all of the game. This isn't a pure shooter, the goal isn't to get to the end as quickly as possible.
I can half agree with some of oversimplification complaints. The unified ammo is lamentable and the lack of Spector's innovative skill system is regrettable. I hacked around the ammo with a simple ini tweak that simply fills my ammo full when I pick up any clip. (I'm playing on realism mode and it's standard setting empties your ammo pretty much after any fight). The lack of skills isn't really a negative to the game as it plays, but if it were included it would expand the replayability even more.
I had no problems with the GUI or the Inventory screens at all.
I do regret that Ion Storm fiddled with the renderer so much. Yes, some of the scenes look great - but it caps the performance too much and was apparently the root cause of no DeusED being shipped. SP and side missions would be fun to make here.