You can vote for up to 4 games, and you can change your vote if you want. The poll will be closed nearer to the event.
Here is some additional information about the games:

SpeedRunners: http://store.steampowered.com/app/207140/

Lethal League: http://store.steampowered.com/app/261180

Starcraft 2 - Gem TD: http://us.battle.net/sc2/en/forum/topic/3280530671

Ricochet: http://store.steampowered.com/app/60/

Rocket League: http://store.steampowered.com/app/252950/

Unreal Tournament 2004: http://store.steampowered.com/app/13230/

DotA 2 - Pudge Wars: https://steamcommunity.com/sharedfiles/ ... =296831818

Quake: http://store.steampowered.com/app/2310/

DEFCON: http://store.steampowered.com/app/1520/

Hotline Miami 2: http://store.steampowered.com/app/274170/