That's more or less up to you just because I don't know it, yet. I think the regular stages resp. their loops could have a distinct melody like in Mario games or SNES games, but with deeper tones and (more) bass and maybe even a little touch of techno or sth. like that. I don't want to have 8/16bit sound, though, the tracks should be accomplished with modern technology and have a clear sound - I f.i. dislike Cave Story's music, it's just too old school.


Things I like that may inspire you:

Super Metroid - Theme: http://www.youtube.com/watch?v=LhAQfpbsymU (fantastic)
I love most Metroid tunes anyway, including the following: http://www.youtube.com/watch?v=WLLE_PvJ5mY&feature=related
One level plays in a big temple, I would like to have a song that was somehow inspired by the following two tracks:
http://www.youtube.com/watch?v=QQCZIb0fbt8&feature=related
http://www.youtube.com/watch?v=ghCbnFbpbF8&feature=related (quality is bad, it's a GBA game)
Another Metroid track, the Ridley battle theme: http://www.youtube.com/watch?v=eBMSZpWPvDI&feature=related

Super Smash Bros. - Dreamland: http://www.youtube.com/watch?v=opbqLIrUHuE&feature=related (melody is awesome)
Many Tetris (and Mario) remixes, including: http://www.youtube.com/watch?v=CosNJBante0 and http://www.youtube.com/watch?v=ZDfb78ZmXYI
SM Galaxy 2 - Puzzle Plank Theme: http://www.youtube.com/watch?v=keeM4wFRJWk (I know, pretty complex, but I like it)
Deadmau5 - Ghosts n Stuff: http://www.youtube.com/watch?v=FL909DN4c3g
Fancy Mike - Death Proof: http://www.youtube.com/watch?v=3_lc6b_A33w
YKEL - the Future Mix: http://soundcloud.com/ykel/ykel-the-future-mix-2011 (sometimes a little too much dubstep)

The following three tracks have vocals, they are regular songs, and don't fit a video game, I know, but I like their sound:
Totally Enormous Extinct Dinosaurs - Garden: http://grooveshark.com/#/s/Garden/3wEJLC?src=5 (sounds like a video game after all)
The Black Eyed Peas - Whenever: http://grooveshark.com/#/s/Whenever+Album+Version/3TFFgB?src=5
Chase & Status - Time: http://grooveshark.com/#/s/Time/3YYyvZ?src=5


Btw. I like your track, esp. after hearing it for the the second/ third time.