Yeah, it might well be TOO old to play.
Barring multiplayer games whose community has moved on, and games that rely entirely on novelty appeal, there's no such thing as a game that's too old to play. The graphics of any given game are EXACTLY the same today as they were originally. Sometimes better. If gamers in the year 2000 could genuinely appreciate Deus Ex and System Shock 2 without needing Crysis-level graphics, there is absolutely no reason that should bar anyone from playing such a game today. This expectation is completely artificial conditioning.
And it's DEUS. Not Dues. It's Latin for deity.
I disagree on a certain level. Because someone (for instance me) is used to good graphics, or a graphics standard that has been improved alot since 2000 if you will. When i load up and old game like Deus Ex, and it has no nostalgia factor for me (never played the game before), the graphics are a turn down for me. While gameplay wise it might be a good game, i like a good looking game. It's just what im used too.
The argument that because people could enjoy it then, they should just as well be able to enjoy it now is a crappy argument imo. For some this might be valid, for others it is not. Standards change. So games become outdated to me.
As mentioned, nostalgia can be a factor here. Other old games i played when they got out, i still like to play. They seem far less anoying for me to play. Even though the graphics are crappy. I didn't like Deus Ex at all, but i ocasionally still enjoy a game of Splinter Cell 1 or the first prince of persia, or the old 2D GTA, the old jedi knight series and many more.