It seems every week these days another mega, must play demo gets released. Most of the time you will see that a demo is huge and just wait to get it on a magazine cover CD, or until the next LAN. The last top demo I spent ages downloading and playing was UT, I remember waiting up all night, and then getting the demo early and playing it for 2 days solid. The only other time that has happened was a couple of weeks back when the Deus Ex demo was released. I was a fan of System Shock 2, and by all accounts Deus Ex was System Shock 2 with more FPS and less RPG, which was right down my street.
In my opinion Deus Ex has one feature, out of many top features, that makes it stand head and shoulders above all the competition. The feature in question is the ability to tackle problems using a multitude of solutions. In other words freedom of player action, now tie that into the fact that you have to suffer consequences for actions and choices you have the basis for a massive and amazing game. Deus Ex lead designer Harvey Smith said, "We had such a huge problem putting Deus Ex together because it was all on paper...just a concept. A lot of what we tried took a long time to make work as well as it does".
Of course these days no one will ever rule out a sequel, the corporate will be getting their 'milk this for all its worth' hat on. It seems the folks at ION have gone a step further, Smith saying openly, "Definitely a Deus Ex 2, plus two or three other projects currently in a numinous stage of preconception". You would think ION are trying to make money quickly to cover a loss on another game or something!