One of my favourite games of all time. Regardless of if I am playing solo or with a bunch of friends this game never stops being fun. Versus is where the most fun can be found in my opinion, however the various mutations bring very interesting spice to the gameplay. A great aspect of the game is its connection with the Community Workshop. You can change most aspects of the game. Want to fight Shrek instead of the standard tank? Go for it. Want to replace the infected with hordes of cats? Why not? The difficulties feel very balanced apart from the top 2. Easy, Normal and Advanced feel like they get progressively harder with each difficulty level at a steady rate, but once you change to Expert the jump is much larger. I have friends that can hold their own on Advanced but as soon as we slap it onto Expert it's as if they have never played. The only other con I feel is large enough to point out is the difficulty in finding games consistently. Reason being the game is 10 years old now and doesn't have as much replayability as something like TF2 or the Counter Strike series which have been going on for much longer. All in all, I recommend the hell outta this game if you enjoy arcade style zombie shooters. 10/10