There is a currency system in game that helps you purchase new weapons. Your team mates can give you some of their stash and you also gain funds through each wave. There is a nice selection of weapons ranging from melee to explosives and guns. The perk system is set in to help you have an edge on your particular play style. You can have certain bonuses for whatever area of expertise you want to specialize in at the time. This can be changed in game and during your visit to the merchant, if you make it.
The difficulty fluctuates each enemy wave and the number of enemies continue to grow. The enemies vary more as you progress also. You start with your run of the mill zombies and work you way up to the main bad man who is a beast to kill. Some enemies are armed with melee weapons while some have a rocket launcher.
The sound track is well mixed and entertaining to listen to as you play. The sound effects are also good quality.
The only short coming I have seen in this game is the dated graphics but that being said I still enjoyed this far more than LFD. It's fast paced action and it keeps you on edge even in between hordes as you rush back to the merchant as fast as possible.
I recommend owning this one over LFD. This is my happiest buy in a long time. Buy it and good luck making it to the merchant in time.