This game literally does EVERYTHING correct.
Style and Story wise, this game is priceless! A guy stuck in a trench, getting upgrades from nowhere and some how getting all of the funny things that the enemy forces say! I seriously love a game with a sense of humor and this one just has it in droves.
The gameplay is where this story succeeds the most though, in that while it is heavily repetitive, it is catchy and fun, and there really is nothing more fun to do than shoot at endless waves of enemies.
The thing that I love about this game, that a lot of games seem to fail to do right, is that it makes this challenging but not rage inducing. I recently played a game that was fun to play, but in the end got far too frustrating and impossible for me to enjoy anymore. Not this game though! There were a few times were I was beaten, but it was because the fight was challenging, and when I overcame the challenge, I felt good.
This game does everything right. It's funny, well made, and can be played for hours without getting annoying or tiresome.