It just stopped for me as well. Wave 3 was the last for me I thought but maybe it was 4. I did not figure out the inventory. It's still a full game. I'm using a touchpad so the controls are awful. I'd love to use a controller with it.
However I do have to say I found this closer to an arcade game than a roguelike. It would have felt more like a roguelike to have the arena be a maze of some kind allowing exploration.