It does play OK.
Its meant to have 60 screens instead of 20 IIRC. Those being two extra 'sets' of levels. However the cheat to activate them does not appear to work on emulation. I'm not sure if this is the way the emulator (more accurately the PC keyboard I guess) is read or something else.
Hmm? I thought you just pressed 1, 2 or 3 at the title screen to choose a level set.
The game lacks the charm of the Spectrum version in my opinion. I really dislike the conveyor belts, in particular. I’m unsure whether any of the differences in the game engine have any great effect, especially regarding pixel-perfect jumps. I’m not really sure such a huge speed-up is a good thing, and MM is tricky enough without it. It’s “OK” but as with many MM and JSW ports, it’s not as good as the original.