LOVE XCOM, the original is such a classic.
I played Invisible War on XBox, always intended to play the first but never got round to it.
I picked it up a few months back, and yes it has aged a lot. The graphics suck and it is amazing how much gameplay has changed. I found the shooting far too frustrating, and I knew I would never finish it.
So I cheated, and I NEVER cheat at games. I'm not proud.
But it did allow me to finish a game that I otherwise never ever would have done. And I'm glad I did, because Deux Ex really does have a fantastic story, some great settings, and wonderful mechanics. I just needed an unfair advantage to compensate for the game's inherent frustration.
The main problems are that as an FPS, the hit detection sucks, and you are seriously underpowered at first, and as a stealth game it is too dependent on luck.
I would say get Deus Ex, unless you know you are a fan of the XCOM genre of strategy. Deus Ex has broader appeal, but if you are into the XCOM genre, there is little better...