I'm very impressed. I've just tried this out for the first time, and it's absolutely great. The graphics are LOVELY – some of the best I've ever seen on the Electron. The design is extremely colourful and attractive, the motion is smooth and everything's properly masked, so there's none of the ugly EORing that you so often see when sprites overlap (the BBC/Electron's answer to attribute clash on the Spectrum!). Overall, this colourful game makes fantastic use of the Electron's graphics capabilities.
As for the game itself… it's pretty simple and straightforward, without a lot of depth, but that's not a criticism. It's obvious what to do, and it's good, playable fun. (And with graphics like these taking up so much memory, you can't expect too much RAM to be left over for deep gameplay!)
On my first proper attempt I collected about 40 stars, so I must have got nearly halfway. That's encouraging: the game now feels like a challenge, but not an insurmountable one. I've yet to see anything that seems unfair, or that I couldn't master without a bit of practice. I like games that are reasonably challenging but winnable, and this feels like one of those.
Two small criticisms, both of them very minor:
1. If you want to jump a gap, and Zezito has a solid block right above his head, the left/right movement stalls when jump is pressed. It's not a problem, but it feels awkward and unexpected. If it's not possible to jump upwards, I don't think that pressing jump should have any effect on left/right movement.
2. There's quite a lot of instances where you have to jump between platforms across screen boundaries, and it can be particularly awkward when jumping from the top of one room into the bottom of the next. Unless the keys are held down, the left/right movement can be forgotten while the screen is redrawn, leading to you missing the block you were aiming for and falling back unexpectedly. But if you keep the keys held down too long, you may move too much on entry into the upper room, and perhaps move into a killer object or fall off the ledge you've just landed on. I'm not sure how best to fix this, but it's the most awkward aspect of the gameplay I've found so far. You do get used to it, so it's not a big problem, but it could be improved.
Overall, though, this is fantastic, and a great demonstration of what the Electron is capable of.
The one other thing I'd really like to see is a dedicated BBC version of the game, probably with better sound (maybe even a background tune) and obviously speed-adjusted for the more powerful machine.