The first thing I was surprised about was the accuracy of controls. When playing many 8-bit games, there's a noticeable lag in inputs, and games are often designed to allow for this. Some games did this better than others - Titus the Fox, for example, allowed a bit of leeway in jumping. That's not the case here, but the response to inputs is instant, making you feel much more in control.
The second thing I noticed, after playing for a while, is how complex the game is. It's packed with puzzles, in terms of finding new rooms, finding ways to attack enemies without taking damage, and exploration. I originally thought that the fact that enemies can't attack you while you're standing on a crate was a limitation of the game, but in many cases it's the very basis of the puzzle.
That's not to say that the game isn't an action-based title. I've not completed it yet, because the five lives you start with don't last long when you're being attacked. I shall try again, though - each time I play I get a bit further. I may need map paper soon though ...
Meanwhile, I loaded up an emulator to take some screenshots, and took the opportunity to compare the GX4000 game to the CPC version. As I said above, the disk version seems to chug a bit more, which may be loading, but the main difference is the visuals. Look at them, it's an astounding change.
(GX4000 is the top, standard CPC is the bottom.)