Invisible War wasn't that bad. The mistake was putting the Deus Ex name on it. Release it as a stand-alone game and you've got yourself a solid 8/10 action game. Make it the sequel to DX and, yeah, anything short of perfect perfection is FAIL. It's not fair but that's how it goes.
I began to wonder a year or so ago if maybe the passage of time hadn't distorted my impression of DX, that possibly what I remembered and what I actually played were two different things. So I fired it up again and played it all the way through (thank god for WinXP) and you know what? It was great. The voice acting and graphics were pretty bad but I stopped noticing that about ten minutes in because I WAS HOME, BABY! You want proof that hot visuals don't make a great game, DX is it.
I don't recall being forced to fight anyone in Thief or Thief 2. I remember getting into a few throw-downs with Karras' children when I wasn't careful enough, and I'd usually shoot my way through zombies just because I could. But I don't think I was ever forced to fight people; in fact, many of the game's levels (at least on expert mode, which is the only way to play) don't allow any contact with enemies at all. You fight, you fail.