I disagree. I like Thief, I love System Shock 2, but I don't care for Deus Ex. Deus Ex feels like a lesser version of those two games to me. Both stealth and combat are horribly awkward and neither feel good to do. Stealth is hampered by wildly inconsistent AI and the lack of any reliable takedown maneuver, so oftentimes I'm save scumming past every single guard. I get what they're trying to do with combat in that you have to level up those abilities in order to effectively fight back, but it feels so slapdash. And that's Deus Ex's biggest problem for me. The game has some amazing ideas; I love the concept of deciding whether to stealth it up or go in guns blazing, and I adore exploring the levels to find new and interesting ways to accomplish your goals. It's just that the execution of those ideas leaves a lot to be desired.
It goes like this: if I want to play an excellent stealth game, I play Thief, or if I want to play an immersive RPG with different choices on how to approach combat, I play System Shock 2. Deus Ex tries to do both but doesn't do either all that well.