In the most recent Bombcast, Jeff describes the appeal of stealth games as being the "thrill of taking out a dude from behind". Which while true as far back as the original Thief and Metal Gear Solid, is not always the case.
And in the case of something like Deus Ex: Human Revolution, I found it far too easy to just knock out the entire room with silent takedowns and tranquilizer darts and it's not even a challenge because it's really just all about "how can I isolate these guys and take them out". You were too good at taking dudes out in that game (and most recent Metal Gear Solid games).
On the other hand, there's a level in Alpha Protocol where you sneak into a CIA safehouse/listening station thing in Rome to plant a bug, and you get an extra bonus if you never even knock out a CIA agent, because then they have no reason to even suspect anyone was there to plant a bug. Getting in and out of that mission leaving zero trace was actually super satisfying, even if it just meant being really careful to dodge about 3-5 CIA guys. Hitman has had varying degrees of success with that idea, although more so in the earlier games.
So what are your thoughts? I liked stabbing dudes in Mark of the Ninja as much as the next guy, but oh man, finishing levels with the Path of Silence suit where you have no sword or lethal gadgets is wicked amounts of fun.