First of all, thanks to all the commentators for your feedback! It was all very helpful.

I have tweaked the game and hopefully it runs a little faster, but there is still lag. 

I've updated the platformer to use Hauntology's Platformer Plus so there is now some coyote time and a small jump buffer.

I've upgraded the pick ups to not only give score but an additional life, to make things a little easier. I stuck with the lives feature because I wanted the game to feel like an old arcade game.

There is also a .gb rom file to download now.

At some point I will make a new bigger version using GB Color mode, which as well as running faster will suit the game better I think as it could do with some color! For now I'm going to leave this version as is.