I enjoyed the first run a lot. The visuals of the clothes disappearing, the slime covering the body, then the full transformation were all great and flying around in zero gravity was was absolutely very fun. My first run I wasn't all too concerned with removing the goo and finished fully transformed and I had a lot of fun, but when I tried going for an untransformed run it became a lot more frustrating.
It felt like there was too much goo directly in the way, with not enough boxes to maneuver around unless I got lucky and a box came flying by. The box thing really felt like a problem when I got to the areas covered in slime walls, specifically the start of the maze area and the zigzag area at the end. It felt like I had to be either flawless everywhere else or flawless in these areas. I would try to zoom past what feels like way too many of the moving slimes at the start of the maze to not get completely covered, only to start slamming into the walls and get covered anyways. The zigzag area makes it feel like I have to utilize every box that I have perfectly, and even one mistake is a reset back to beginning. Also, I don't know if I'm just crazy or if there is some sort of hidden mechanic that causes the transformation to go faster, but it ended up feeling like the transformation would become too fast to remove the goo in time, even with only one layer of goo and a lot left to transform.
All of that combined into an experience that felt frustrating and sometimes boring to me, as I felt like I could never get the speed quite right. I would either slam straight into some goo or I would fuck up with a box and would be left slowly floating until another box came floating by, unless I missed that box in which case I would have to keep waiting for another. I might try it again at some point and see if I can get a successful untransformed run, but not right now.