The number of people playing will have alot to do with the waves of people being let into the beta. since it is so short people will play threw it once or twice with toons they want to play then set it aside.
My biggest gripe is that 80% of the time it won't let me hit the join public game button, because apparently I'm the only one out of 100k people that wants to do a Black King run. When I finally do get into one, it's always me and a partner, never 3 or 4 people. However, I have invited 2 people from friends list to play a game and all 3 of us were in one.