The initial scene is really well made, and It does feel like being far away and lost. The entry to the "arena" is really cool too. Upgrade system feels fair and the addition of rarity levels makes it even more interesting. I found myself upgrading stats instead of healing just because the upgrade was "Tier 3" quite often.
That being said, there are also a couple of improvement oportunities with the shooting mechanics. The first one would be a change in the crosshair because it gets easily lost in the background, and I didn't know where I was shooting quite frequently. The second one is the more visual feedback of the hit, because whenever I was shooting at the enemies I was honestly just hoping I was hitting them (happended more often with the big ones. I noticed skeletons have some red particles when hit). Didn't stop me from playing, tough. The game is really fun.
Good job!