Hi, thanks for playing and for leaving detailed feedback! I'm glad to hear that you enjoyed your time!
I started playing with mouse and keyboard, and had a bit of trouble keeping my aim on the bosses as I would sometimes lose track of where the targeting reticule is. When aiming with the mouse, the reticule's positioning is affected somewhat by how the scrolling will lock against the boundaries of the map.
Yeah, I've made the aiming ridicule larger a couple times and I'm fairly convinced that losing track of the mouse in the chaos might be somewhat unavoidable for new players. I think it's the kind of thing that one will get better at after playing for a while.
I'm not sure if 100% understood the second sentence, I think you're talking about how scrolling the screen will move the mouse along with it? It might be interesting to experiment with an option where the mouse cursor stays still (relative to the game world) when the screen scrolls, but I think something like that would be less than ideal for anything except a relatively small boss arena.
I experienced some dropped frames and performance fluctuations on the first boss as it got closer to defeat.
Good to hear that other than this, it was smooth for you. The last phase of the first boss is a problem area, it's my go-to scene for benchmarking right now.