I couldn't play it when it came out, because my computer didn't have the horse power, but when I found it on sale a few years later I was thrilled. It was the perfect setting for me, a bleak future, sci-fi, cyberpunk... But when I think back on playing Deus Ex I only remember frustration. I just couldn't get used to the gameplay; I was never able to effectively sneak, and the fighting was even worse. It took seconds to line up a shot, while the enemies were running around (with no regard for inertia) firing at me. The weapons felt like they didn't have any weight, and were ineffective, and everything i blew up seemed like it was made of hollow aluminum. This of course could be down to the fact that my character build was off. It's been nearly ten years, and so far I've not been able to get myself to play the game again.
I've played some of Invisible War but didn't really get into it, the only thing that stuck with me was NG Resonance's music (it's by a band called kidneythieves). Human Revolution on the other hand had a slight case of consolitis, but was an all around solid game.
As far as classic FPSs go the gold standard for me is Half-Life. Yes, it's a linear corridor shooter, but as far as gameplay goes it is unsurpassed for me. Honorable mentions go to "The Operative: No One Lives Forever" and "Tron 2.0", both by Monolith.
So much for rants. 
I have a really hard time putting into words why I found the fighting in Deus Ex so painfully frustrating, and I often feel like the only one who had that experience...
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