Some games just impact me in a way that others don't, and I rarely go back to games for that reason. Another example is that I've probably spent longer thinking about Thomas Was Alone than I actually spent playing it, it's a very short game that had a tremendous impact on me.
Deus Ex was the right game at just the right time, and somehow the sequels never recaptured that magic. For me, a large part of that was precisely the promise the game had, even if upon technical breakdown it didn't really deliver on those promises. The idea that you were affecting and interacting with the world. The idea that you had a full gamut of options of how to achieve a mission. These were promises that weren't well kept, but they kept the imagination alive.