Given that the signup button is the only thing visible, well, this is going to be a pretty quick review.
When I clicked the link and it asked me for authorization to access my account, I hesitated. I went back to the link you provided to see if there was any information regarding what this means and why I should do it. In particular, I would like, prior to authorizing: descriptions of (1) the game itself (2) what impact it has on my Twitter account.
To gain back virality let players gain points or money or whatever on a per tweet basis. I'm sure you already do this.
Which brings me to my next point..I don't know if you do this, because I signed up and tried to play and I had no idea what to do. Granted, I'm probably not your target audience, because I've never played these types of games (Mob Wars, Youville, etc.)
Basically, you've got to boil it down either on the splash page, or the initial load (maybe with a modal popup), if you want inexperienced users, who don't have hours to investigate, to play.
Guess I learned my lesson.