Pros:

Feels like a mario map

Cons:

Plays like a platformer, which L4D2 is not
Buttons are in confusing places
Buttons occasionally don't work
"Gotcha!" mechanics

Conclusion:

This was really frustrating to play through. I went in with a team of four and we had to play it multiple times to even see the boss, who we were unable to defeat because what seemed like the "final" button wouldn't depress, and the boss just wanders around the room doing damage that you can't avoid. There are also fake walls and ghosts that come out of the walls that can OHKO you for no reason and without warning, and the platforming is awful. It's comparable to trying to make an FPS out of the assets of Super Mario Brothers.