great job for a first game!
keep on practicing... best thing to work on is ur hittests. its kinda glitchy at those parts where there are like lots of tiny platforms. besides that are you using vcam?? if u did try to do scrolling bg its less lagg =D
variable jumping (longer u press up = higher u jump)
more environment interaction
thats what makes platformers stand out.... jus add a wall jumping engine to a clean cut platformer... ull get a frontpage game.... imagine that + many other environment interactions.. bwahahaa