I'm enjoying IW a lot more than I thought I would after playing the demo. I'm still kind of bummed out that so many of my favorite aspects of DX1 seem have to been tossed out the window for the sake of simplicity, but for the most part, I think the developers have done a decent job of creating an interesting, open-ended playing experience. The game just lacks the polish of minor details that helps to really emerge the player into the game's world.
One thing that's really been bugging me, though, is the apparent lack of the trademark Denton "non-lethal takedown." In DX1, it normally took several whacks of the baton to take down a NSF or MJ-12 trooper, but if you snuck up on them and delivered one, solid strike to the middle of their back, you could get a silent, one-hit knockout (or kill) with just about any melee weapon. I thought this feature was extremely cool, and it's sorely missed in IW. So far, I've been relying on a tactic by which I give them a good shock with the riot prod and then smack them in the head repeatedly with the baton. I guess it gets the job done just the same, but it's not nearly as badass (and what's with the riot prod, anyhow? That thing doesn't deliver nearly as strong a shock as it should). And it's not really silent, either; even a guard who's just been shocked with the prod will still yell out (though apparently no one hears him), and he'll still almost always draw his weapon on you before you can bring him down.
The one-hit takedowns of DX1 provided a tangible incentive for playing stealthily, which I feel is missing from IW. It allowed players to quickly and silently eliminate enemy resistance. Especially early on in the game, when your skill with weapons was generally pretty poor (another thing I'm missing in DX2--perhaps not necessarily a skill system per se, but some sort of measurable progression in weapon skill), being able to knock out a NSF trooper was a valuable ability, since even one of them could give you trouble. IW provides you with no such incentive.
If I might digress a moment, I'd like to make one more somewhat obscure observation before I call it quits: I just don't feel like nearly as much a badass in IW as I did in DX. JC had attitude, and he had quite a few well-written, intimidating, very cool lines of dialogue. IW perhaps provides a more open-ended approach to navigating obstacles (the ability to knock out laser trip-wires or block them with objects, for instance), but it offers much less appealing methods for dealing with adversaries. There were say many cool ways to fight in DX; if I came across a MJ-12 trooper guarding an office, for example, there were dozens of ways I could go about eliminating him. I could pump him full of lead, or blow him to bits, or scramble the nearby security bot, or turn the room's turret against him. Or, if I wanted to go about it stealthily (and non-lethally), I could throw a gas grenade into the room (which stuns in DX, unlike in IW) and then bring him down with tranqulizer darts while he's still under the effects of the gas. Or, one of my personal favorites, I could pepper spray him in the face and then prod him. Granted, you can do a lot of this stuff in IW too, but there just don't seem to be as many innovative ways to own biatches as I would have liked.
Okay, I'm done ranting.