Well lol
They could've hired you to write it, but do you know the first thing about actually "Writing" music? Lmao, this is a MIDI to MP3 remix as stated in your description, so technically you didn't "Write", you "Covered" it.
Sounds like FL 7 (or 8) with the Inferno Guitar used as the lead, one of the Electric guitars from the Sytrus plugin used for the rhythm guitar, and I think you've got a soundfont for the drums (or it's the FPC one), but I might be wrong :P Bass, I have no idea lol, but it works :P
Anyway, I never rate MIDI to MP3's higher than 7, because really, they don't take much skill to make... Now, had you changed something, say the drumline, or added a solo here and there, I'd be able to rate it higher, but sorry, no can do.
Overall, not too bad, good choices on the instruments, they sound good, but really needs some more originality... And no, I doubt you could "Write" a better song, remix one sure, but not write one ;)
That's it :P
~DJ-HappyFace :)