Deus Ex hasn't aged terribly well in my opinion. The gameplay is fantastic, so I still play it - and still love it - however its hard to honestly recommend it to someone who hasn't already played it, at least a little. The visuals alone are pretty off-putting for someone new to the game, let alone the terrible A.I. and other quirks we've all come to appreciate after numerous sessions with the game.
In any event, it should be noted that Deus Ex still remains the best game ever made, and any one who considers themselves a 'real gamer' needs at least one play-through under their belt to be taken seriously. It's really hard to emphasise just how incredible that game was, and still is.
From all accounts, Deus Ex: Human Revolution looks to be _this_ close to the original, with only a few items holding it back - most notably the god-awful Boss Fights.
As for Thief 4, or Thi4f (seriously?), I suspect it will go the way of most stealth games, and add a heavier action component. I'm replaying Thief 2, and frankly I couldn't see a modern publisher pushing that kind of title out of the gates, when Call of Duty is the number one title on the planet. I'm getting ready to be incredibly disappointed.