I recently finished Deus Ex: Human Revolution, and I thought that the entire game really started to tank near the end. I'm not entirely sure WHY, but it might have something to do with the fact that I was playing the endgame after revisiting Detroit on godmode, since I had around 100 bullets for my exploding-round revolver with pin-point accuracy. The last boss, while visually interesting, was mostly nonsensical, COMPLETELY unexplained, and just about the easiest thing in the game. Maybe it had something to do with the fact that I had an overheating-resistance plasma rifle with over 200 rounds, along with a dozen stimpaks. The ending-ending itself was alright, but it didn't feel like there was much weight, again, perhaps due to how the game played near the end for me.
Though it's similar to the ending of Deus Ex and Mass Effect 3, as others have pointed out, Deus Ex's endings were actually pretty interesting and coherent (implying that those of ME3 were not...), and fit the ideas and themes of the game quite well. The ending-endings to Human Revolution weren't quite as good for me personally, but they weren't BAD, and again, they were coherent and fit the themes and such of the game.
On a side note, for future reference, how do I make the spoiler tags that people have been creating throughout the thread? (I'm a bit new to posting here.) Is there a link to somewhere on the website that tells how that I have overlooked?