L4D2 is an okay game. The characters are not as great as the last installment and the daytime levels feel like a drone (a lot of the music does not help this fact). The story actually follows a narrative arc, but there are only a couple of maps that are any good.
With the sequel came about new guns and new zombies, the majority of which can be filled under the “ZOMG BS JOCKEY WON’T DIE!!!!!” The melee weapons are a welcome addition as well as the SPAS combat shotgun (my favorite).
In my eyes, the only thing that make this game better than L4D1 is that it seems like more people are playing L4D2, and the mutations. Scavenge isn’t all that great and Realism is really a try once, but get bored and never play again.
In the end, unless you get both L4D 1 & 2 for the price of ~20, then you might as well just skip this version.