This is quite a cool game with an interesting concept - I've never seen anyone use a Casino Theme for a tower defense, so well done! The casual music suits the Casino theme quite well!
It would be nice to be able to pause the game. Level 2 doesn't seem to ever start for me. While I saw the information in the main menu, it would be nice to have parts explained while playing(e.g. what towers do being explained in the store).
There also is a bit of a lack of feedback - until I read in the info that when you have 3 of the same towers merging into one better tower, I was quite confused when all my towers suddenly disappeared. Maybe a sound or particle effect to show this would be better.
Also, you can place the towers slightly outside of the game board, which was a little weird. That, and the game's lighting is a little dark and sometimes hard to see.
Other than that, I really liked this, and hope you develop the idea further! Good job!