Well I would say, get Deus Ex.

I have been replaying this game again the last week and wanted to open a topic for it before I saw this one.
It is definitely one of the better games even if the graphics are a bit older now, a lot of freedom of how to decide to go through a level and an excellent storyline.

Unfortunate the sequel is sort of opposite, it is perhaps good for one run through but I don't think you will come back to it.
I have been playing the game again and it really feels like a task and not something I enjoy playing.

In case the graphics of Deus Ex 1 are really an issue for you, wait for the HDTP pack that is under development.

In case other people like me would like to enjoy Deus Ex 1 again but have a somewhat different experience, people are working on a mod called Revision.
The storyline is the same but the levels now have a different lay out.