The scroll image, and text area, for the credits and tutorial could use with being wider to make things more readable. The font size feels rather large for the space, though you wouldn't want to go too much smaller for readability. Extra width would help a lot, even with the large font size.
The game was simple and easy to understand. There wasn't that much to do, so it did feel like the player did not have a lot of control, and most of the game was luck. The only real choice was when to use the respin, if you had enough. Having played through it, I'd say that if you have enough to respin, and got a bad spin, then you always want to repin, which again reduces this to mostly just clicking the buttons and hoping for good spins. I was lucky enough to win my first playthrough, though barely. My health bar was barely visible when I beat the last opponent. The slot machine concept is neat, and could work, but it needs something more to let the player feel more in control. Sure, a real slot machine doesn't really give you much control, but for a core game mechanic, I feel like it needs something more.
As a first game it is decent. You have a complete and playable game. It works as a starting point, and just needs to be built upon.