Deus Ex is intelligent. It creates a world like ours but also different, weaving together all kind of conspiracy stories and sci fi ideas. You always have multiple ways to accomplish an objective, as well as each step along the way. If you like to find hidden things, this is your game. If you like to find nonviolent ways, this is your game. If you like to shoot it out and kill people, this is your game. Basically, this is your game, no matter who you are. I still love this game.
You know that feeling? The one where you realize after a couple of hours that you are playing a truly great game? That's the feeling I had playing Nox. Its one of the games I remember from this era. It has story, mood, gameplay, graphics, etc. - the full package. It holds up remarkably well. Get it, play it, love it.