While the game does save level and prestige data, biome progress is lost on exit. A bit of a hassle, given the minimum 13 seconds or so per biome - I've gotten two nebulously final end game notifications, both vaguely suggesting that there's more, so I'd like to do some deep dives. With the biome resets, that means ((13x100)/60) seconds (over 21 minutes) of doing nothing in order to reach biome 100, the approximate point where a late game Hollow isn't just killing everything before it even shows up on screen. Coupled to how quickly XP rewards and requirements scale, those resets where a high level character goes back to biome one feel like empty time - no threats, no rewards, just waiting.
The victory screen(s) read like they're aiming for mysterious, but land closer to 'self-contradictory'. The Hollow Run is over, but there's more to the game, and the Hollow will continue to Run? I don't know if I'm done, or if there's an actual ending, and the writeups aren't clarifying anything.
Gripes aside, good use of two experience layers/ level trees, well balanced options. Actual decision making for the player is somewhat minimal, but is there, requiring some thought over which option combinations synchronize best. No noticed bugs, aside from the biome loss detailed above. Good job on this one!
