Pros:

Most are realistic.
Some are funny.

Cons:

Some of the images are too clean and crisp which takes you out of L4D2 immersion.
Some are too low quality and unpleasing to the eye.
There's nudity. Not a bad thing per se, but it's not in the description.

Conclusion:

Although most of it is good, the mixture of bad quality and super-clean/HD images just take me out of the immersion too much for me to leave it as a permanent mod.