Mmk so I've been playing the hell out of this game for the last week. It is INSANELY fun and challenging! I love the robust upgrades and each one you can clearly feel he upgrade. This game requires not only a good balance in upgrades but also planning ahead. My biggest problem late-game was fast moving dudes that would overlap with you so you couldn't hit them. This leads to having to up your speed and at even later levels, the super fast enemies can have a lot of health or damage, making them even more lethal.
There are a few drawbacks though that I'm not 100% sure what to do a bout but owell.
The game gets pretty repetitive. It' easy to be in an arena where yo barely get any XP and your only choice is to go up in arenas but that leads you down the rabbit hole of the enemies being more dangerous but the game is still kind of stagnant.
Other than that, this game is brilliant and I've had loads of fun playing it.