Thanks for taking the time to try out our game, and I'm sorry to hear you were mostly frustrated when playing. We're already working on improving combat, and it will be in update number one post jam. We're confident this will tackle the central issue with the game, as well as many things that derive from that.
About the checkpoints, they're meant to reset your spawn location, they don't touch any progress made (upgrades and new abilities), or any major door on the map. So, maybe you could help out by trying to be more specific with the way you lost loot and abilities? They do reset some levers and triggers, which require the player to solve the mini puzzle again; this will also be balanced better in the future. Again, reusable checkpoints that restore HP and charge will be there from the first patch post jam.
It sounds like you took the time to play at least up until the player gets the Fireball, which is a good 15 to 20 minutes into the game. So that tells me we do use common sense, otherwise you wouldn't have spent all that time playing. We are aware of most of the issues so we'll learn from our mistakes and improve thanks to great feedback from a community built around supporting each other. Jams are usually all about learning.
So again, thanks for playing our game and for the valuable feedback you seem to provide with your comments regularly, it's greatly appreciated. Feel free to check back in the future if you would like to try the game again.