It's a pleasant song to listen to, but it doesn't evoke a feeling of frantic action. This would be perfect if Contra ever went into a strategy game, or if the level were one of slow progression. Unfortunately, the song is just too mellow to catch the feeling of the game. Perhaps working on a faster-paced remix is in order?
I kept waiting for something to happen in this mix, and it just never did. I've tried to remix this song myself, but it's a really difficult one. Try to vary the beat and maybe freestyle a bar or two using pads and arpeggios after playing the theme once or twice. Can go a long way into making a remix unique not only from other mixes, but from the original track. Keep working on it!
Please contact me if you would like to use this in a project. We can discuss the details.