http://steamgames.com/tf2/heavy/
I know there are a few people on here that played or still play this game. Honestly, I just got into it about a month ago, and play with some guys I know from work.
For such a simplistic looking game, there actually are a lot of interesting things that you can do in the game.
Anyway, there is a Heavy update next tuesday. So that will be 3 classes with unlocks, and they are adding a few new maps as well.