Happy new year everyone!
Thanks for the kind words, it's really encouraging.
About the difficulty levels, I'm actually deliberately going for something resembling super meat boy, difficulty wise at least. Here's a good article by Ed McMillan as a point of reference supermeatboy.com/13/Why_am_I_so____hard_ (they have pretty cool game design advice over there, so worth a read).
Of course the important part is to make the game challenging/difficult without it seeming to be the game's fault. Basically, being difficult without being annoying, which needless to say is a hard task.
My idea here is to make each level rewarding to the player. Each level will have unlockable items, the game will also feature some RPG elements (the player will be able to spend some of the stars that were previously collected on some abilities and so on at the end of each level) and a couple of other things.
Level design is also something very important. Meat boy for example feature very short and kinda "to-the-point" levels. I might try to emulate this somehow.
Thanks a lot for the very thoughtful reply! Thanks for pointing out the double jump thing, I'll fix this by allowing wall jumps in later versions. I've also thought a lot about the "darkness" that surrounds the player. I've actually tried changing the background to something a little less bright, however I didn't really like the outcome as the colours seemed a little washed out. I will probably go for a more transparent look to the fog, thanks for the suggestion.
Cheers guys, btw I'm almost ready with my little multiplayer demo, I'll be posting something in the coming days.