Poor marketing...
Honestly I don't know what to think of the game. The problem is there's nothing to lure someone to actually check out the full version. Perhaps giving us a story, or showing us what some of the gameplay elements will be in the further levels. Though I understand that you could only have one level, the way-too-simple gameplay and abrupt end to it means that its just a way too short demo for a game that doesn't look very fun at all.
Also, you say that the full game could take 20-30 minutes, but how?Giving us some idea of why it will keep us playing for that long is the sort of thing that will help sell this game.