Very addicting and satisfying game! I enjoyed it a lot! :)
Luckily, I read early on that I should look for the upgrades as they add more interesting choices and make the experience even more satisfying. I really like the idea of moving the slot to decide how you want to distribute your luck. The background and custom UI elements are really neat and watching the balls fall feels very satisfying!
Just a few thoughts on the game: I was a bit disappointed that once the countdown ended, the remaining balls immediately stopped counting. It would have been nice to see the last ones finish falling into the slots. Adding special abilities to the balls, like splitting into two on impact (maybe even splitting into smaller amounts of wealth) or upgrading slots with effects like spawning an extra blue ball when a ball lands there, could add even more variety. Another interesting idea could be giving the player control over when to release the balls and using the number of owned balls as the countdown instead.
Overall, great job! I really enjoyed the atmosphere and the feeling of the game. :D