Nice aesthetics and theme! I like creative, artsy Pico-8 games.
I would say that there are two places that need another checkpoint: pollinating under the guns, and the last part (won't give away any spoilers!). Basically pollinating under the four guns was a pretty good challenge, but having no checkpoint after it means you end up doing it over and over as you try the next challenge (and the next challenge takes some trial and error), and it gets more tedious than challenging.
With the other one (I think it may be the last challenge?) the ones between it and the checkpoint are easy enough, but also get pretty tedious as you try to get the extremely fine movement right with the second laserbot at the end. It is fine movement you need, right? I haven't actually gotten past that yet. The laser is right next to me, but I'm still not high enough.