Hey im designing a 2D platformer game and i cant decide weather to do classic NES style music like that in mario mixed with some other stuff or give it a modern sound, like in newer games.

Get two (or more) tracks in both styles that you like and feel could work for your game then either play (or watch video) of your game with each different track playing. See which one feels more "right" then go with that.

It's a quick and easy way to test out the direction.

What you should keep in mind is that back then composers strived to get the best sounds they could out of these consoles, trying to add personality and realism to their music when all they had was crappy sounds. Nowadays 'chiptunes' are produced by artificially limiting yourself or ruining high quality samples through downsampling or bitcrushing or some such, trying to make music with crappy sounds when high quality samples and effects are readily available, even for free. That's two very different approaches leading to a very different feel to the music.

Just my 2 cents..