Wow I really enjoy playing this! It looks/feels very similar to the original but has a really cool way of implementing the moving trees with that sort of unity energy (that's not bad, I find it very enjoyable).
I guess the only critique is like what kind of choice you want to make with implementation of the trees- do you want the smooth movement of the unity trees or the jerky pixel movement that's actually on the ZX Spectrum? It's weird to think about, but it seems like you did make your aesthetic choice here. With the unity movement.