Cool platformer, though I feel like the secrets should be enabled from the start since I the last one was hidden enough to warrant another playthrough anyways. I also feel like the concept of changing into the circle while on spikes to get a longer jump could have been introduced earlier, as it took me awhile to actually figure out how that worked. There being a portal to the previous level was also a bit annoying at times because I would occasionally jump into it by mistake, which would reset the level.
It was enjoyable enough for me to go back for all the secrets, though I'm not exactly sure what the reward was supposed to be.