Where to even fucking begin? From the top, I guess.
(Disclaimer: I've only briefly played Deus Ex, to the point that I can safely agree with Lyric Suite, it does stealth worse than Thief and combat worse than many other games out there. I am well familiar with all other titles mentioned.)
"Immersive Sim" after a Google search seems to be a genre defined only by pretentious gaming journalists, which have been proven consistently over the past 2 years to be full of shit. I've been dicking around with games (and the various terms they've been called) for 30 years and since it's only now that I'm hearing about this "genre", I'm gonna call bullshit on it to the point that I say that
it does not exist. Any further use of that term will be considered a strawman argument...not to mention just fucking stupid.
I've heard several reasons why Thief ended up being the "idea" Looking Glass eventually ran with as the flagship title for the Dark Engine, but raising cash for an Ultima Underworld 3 is a new one. Not saying that it's a wrong statement, but it does sound like a stretch of the imagination, and one that could do with a factual reference.
Stating that System Shock 2 is better than Thief in any other regard than concerning a few irrelevant details (inventory management, in-game character interaction, antagonist, etc) is grasping at straws. And that's BEFORE we get to the point that the two games barely compare, they're apples and oranges.
Overall I agree with the statement that Ultima Underworld was a more revolutionary game than Thief. The sheer amount of things UUW1 tried to pull off was amazing. So amazing in fact, that the devs couldn't even reproduce all of them in subsequent titles. Example, run and jump against a wall in UUW, then do the same in ANY OTHER FPS (first-person perspective game) ever released...even Thief. UUW gets a "Win!" just for that little detail of real-life physics.
HOWEVER, there are two important facts that need to be kept in mind when comparing the Underworld games to Thief. First, the Underworld games had a series of issues regarding interface between user and game that needed to be addressed. The Dark Engine resolved almost every single one of those issues. Free movement within a 3D environment was finally possible. Second, comparing a game made with the Dark Engine, and a game (hell, any number of games) made with the predecessor to the Dark Engine, is like comparing steaks to fruits: People will quickly question your (lack of) sanity.
In fact, most of Ash's arguments in this thread are based on insane comparisons: Comparing apples and oranges - or steaks and fruits - or the color black and tachyons. You get the idea. Or trying to say that his opinion is no less valid than ours, yet keeps calling Thief fanboys raving faggots and degenerates.
Ash get the fuck out of here; your mouth-breathing rants of futile relevance do nothing anymore than fuel the fires that keep Codexers warm at night.