Guns, swords, explosions and killer zombies. A romantic evening indeed.
The types of games you can play are broken up into two types; Killing Floor and Objective based. The killing floor with its various maps are matches where you are on a map and there are waves of enemies every so often. You make money by killing and surviving, you then use the money to purchase better and more powerful weapons. You do this through all the waves to survive.
The objective based one is simply, you are given an objective (like to X) all the while you get attacked by waves of monsters. Pretty straight forward; it is just a game you play with your friends and try to survive. You can compete for kills or stick to playing smart. The game does also have essentially roles you can play and level them up. For example, you can play primarily melee and the bonuses for that 'class' give melee bonuses such as faster attack speed. Others like marksman would give bonuses for rifles, guns, headshot damage, reload time, etc. So you pick the type of play you wish to be strongest at.
The game is straightforward and simple--the price tag is a bit steep for such a simple game but for what it is suppose to do, it does it well enough. If possible, play it at night with the lights off and headphones on for the best experience.