I was having fun up until red doors were introduced. Not because the red doors weren't fun or anything, but aside from the tutorial, it didn't seem like they were used at all? Like, I literally never needed the pieces in the giant level or the other one with a red door after that. Also, throughout the whole thing, I spent way too much time pushing boxes. It makes me sad, since there seemed to be many more ways to interact with the pieces that weren't explored. So, I guess my suggestions would be:
- Chill on the boxes. Heck, maybe even remove them altogether. As it is now, it feels more like Box Genocide Simulator than Key Forging Puzzle Game.
- Reduce level size. A lot. That should help prevent some of the tedium that came with the larger levels, ESPECIALLY the one with 5 red doors. (Seriously, why did that exist?)
-Perhaps along with that, remove a stage or two of the iron being hot to accommodate the smaller level size?
- Try to focus the levels on funny interactions, like the last level before the red doors (although it seems weird to me that that one had two at once?)
I know this is really critical, but I really do like the idea, and as I said at the start, I was having fun, despite the excessive box murder. I do hope you'll come back to this and revise the levels at some point!