This one paragraph shows you're talking out your ass. You only played the demo, but can completely comment on the entire gameplay mechanics, storyline, and relative sparseness of the entire game from the demo? That first level was literally like maybe 30 minutes of a 20-30 hour game.

If I remember, the demo was Liberty Island, which was one of the slowest, least-fun first levels to a kickass game I've ever played.

Deus Ex used the same engine as UT, so you can't really say the engine was inferior. :p The levels were so much bigger in DEx compared to its contemporaries - an important aspect of the game, and one that it's sequel was rightly lambasted for lacking - that there was no way you could have pushed the same number of static meshes etc that were found in UT and still fit into the available memory of the time.