But it's not worth $20. There are a LOT of games like this and even when those are only like $10 at most.
The graphics were good, the upgrades were useful and the game was fast paced fun but in the end...it's just a demo. I was able to unlock some fun stuff with just the demo, though it makes me hope that people that pay get more unlockable content.
But yeah, this game is not special. These types of games are very common. However, it was still fun to play and I wish it wasn't just a demo.