Conviction isn't as bad as I thought it would be. With sufficient creativity (and patience), it's actually possible to sneak your way through most of the game without killing anyone. However, it's very clear that the designers want you to kill most enemies.
There are a few major annoyances, though. For one, you can't move bodies. Secondly, you can't pick up and throw random objects to distract guards. Finally, guards are extremely paranoid and will raise the alarm if they notice even the slightest thing out of the ordinary. For example, you can flick a light switch on and off, at which point a guard will walk over, look at the light switch and then shout "OH SHIT! FISHER'S HERE! KILL THAT MOTHERFUCKER!!" Once enemies go on alert, they stay on alert forever. While that would make sense if they found a body, it makes no sense for extremely minor things like lights occasionally turning off and on.
The AI detection algorithms are a bit wonky too. You can do the exact same thing three times and one of those times, the AI will see you instantly while other times they won't see you at all. It's also much harder to tell what shadows can be hidden in. Unlike the previous games, the shadows in Conviction are much brighter and you couldn't realistically hide in any of them. You may have two shadows with the same darkness but only one of them can be hidden in. It's even harder to distinguish between shadows when you're hidden because the screen turns grayscale.