This is a well built stealth game, a game genre we are lacking in quality.
You have your choice of several characters, each with unique abilities and unique styles to play through the maps.
What this game offers is more variability of gameplay. If you're spotted or set off an alarm, you have options. You can try gunning down the enemies, running around corners, sneaking behind a nearby bush or running for a vent. It takes time to get through them though, time the enemy can pummel or shoot you. Unlike other stealth games, a well planned out escape won't necessarily lead to death if you're clever.
The difficulty curve is really well done. You're consistently unlocking new content and styles of gameplay with every level, the challenge slowly increasing. If you die, it doesn't feel like such a failure compared to other games because you learn. I actually found it fun to die. While playing co-op, death adds an extra layer of difficulty of: How do I get my teammate back up?
The in game dialogue is clever and cheeky. There is strong depth of gameplay here. I even like the basic 2d graphics, it feels uncluttered and consistent compared to other games. The smaller and quality nature of the maps make the game forgiving of failure.
The bad would be finding enough people to play the later levels with, the few co-op games that lag, and dying on the later levels after an arduous journey through four levels.
I highly recommend the game. I give it a solid 8.5.