This is a special version of Suicide Blitz created by RT Frisk for me to propose to my GF. It took him a long time and I think he knocked it out of the park making it really special. This is the 3rd level of the original campaign that was edited to fit my surprise. The first two levels play like normal to keep it a good surprise.
EDIT: Since my comment was pushed out of the way I will edit it here. She did say "YES" after the "You're Kidding part?", it was just cut off the game since at that point I was already down on one knee with the ring . It was a huge surprise for her since she was not expecting it till late next year. We were playing together in the same room, she is a huge gamer like myself so it wasn't like I made her play a game she has never played before, she actually has more hours clocked in L4D1/2 then anyone else I know. It's her favorite game and the game we actually met through, which is why I chose it as my medium to propose. The game holds a special meaning to us.