I think two words is the average length for game names eg:
Team Fortress
Unreal Tournament
Happy Wheels
Dead Island
Heavy Rain
Dead Space
Killing Floor
Mirrors Edge
But there are games that have three words which are pretty well known eg:
Super Meat Boy
Super Mario Bros
Rainbow Six: Vegas
Worms World Party
And Yet It Moves is four, but definitely try to keep it shorter than "Sonic and SEGA All Stars Racing with Banjo Kazooie"