I have played Resistance and a demo of The Darkness (on the 360). The Darkness has that 'next gen' sheen to it while Resistance is clean but nothing special. There is no multi-player to Darkness, while Resistance just got new maps for online play (and offline too?).
Its difficult to say that the Darkness is a 'thinking man' game, but more so than Resistance. There are some extra ways to play. For example, in the demo there is a room with a couple of guys in it. You have 3 choices: send a darkling in, bust down the door and pop them in the head, or go around to the other side, shoot your 'snake arm' into the verntilation and sneak attack them after knocking out the power. That third one is not obvious so it pays to look around.
The levels I played were also extremely linear. 'Do this before that' kind of stuff. And not exactly a knock to the game, but the main character's voice in no way matches up to the voice in my head whenever I read the comic.