While the game does make use of EXTREME brutal violence, it is not glorifying it by any means. When you are in the mission, you are pumped and not dwelling on each kill, since you are focusing on THE NEXT one and then the next one and so on and so forth. Then, when you are done with the level, you are not booted back to the apartment, no, the music stops being the pumped up fast paced track, and instead becomes a strange ambient track. Almost like going out of a trance, you then have to go back and see the fruits of your labor.
That, combined with the camera sway, and the cycling colors makes it so that the game becomes rather nauseating. Your reaction can go from "hell yeah aced this" to "holy shit this was gruesome". Hell, even in the first level of the game, you are supposed to think that the actions of your character are nauseating, or at least the character reacts that way.
It is not glorifying violence, it is portraying HORRIFYING violence. Same as the movie Drive, the violence in the game is done in such a way as to be rather sickening.
As for the mechanic of having to kill downed enemies, that is a rather amazing gameplay mechanic. You can disable enemies to go for lower risk ones, or to make openings so you can continue your combo, but you have to juggle risk/reward on the fly.