I've only played a bit of this demo, but it seems pretty good so far (very deep). I never got into Deus Ex 1 (the concept of an "RPG-ish" FPS didn't appeal to me at all at the time) but this one seems pretty good.
The first thing that came to my mind when opeining it up was of course "my god this game looks like crap, and it runs like crap too". After enabling a ton of tweaks (I found a bunch of tweaks on some forum that somebody linked to) I can say that only one of my two initial reactions was correct - it only runs like crap. It looks GREAT when you get the graphics configured properly.
First of all is that horrible "Bloom" effect. Yes, it might make stuff look a tad more "realistic" but its horribly blurred and just plain ugly. Turning it off is far more sharp and you can actually see all of the beautiful detail and lighting effects.
Second - this game is unplayable on my machine. Right now it's a P4 2.8C @ 3.25 Ghz, 1GB of dual channel DDR and a GF4 Ti4800. Yes, at 640X480 or 800X600 resolution it runs decent (ie 30-60 fps) in most situations, but in some places it dips down to ~15-20 fps, like the Griesel pit. That is just BS with a 3 GHz machine and a one-generation old video card. I wonder what it's like on a Radeon 9800. I bet at 1024 resolution it would only run at about 60 fps in action-heavy scenes. Yikes.
Hopefully they can improve performance of this game before the final version - right now it plays like a clunky Xbox port (in terms of the graphics, anyways). Also, the default controls suck - especially the Enter key. That should be remapped to somewhere more convenient.