I don't doubt you when you say that it sounds better as a wav, but if you planned on submitting this for a NG competition and you know it sounds like this as an mp3, why not try to remaster it based on the limitations/characteristics of the mp3 format? That's my main complaint and suggestion.

I also agree with Slayer about spicing it up with extra riffs, and the kind of mixing changes to make. Other than that, I'm no expert in this genre. This is all just audio design tips.

Also, it depends on what kind of speakers/headphones one listens with. If you have something super high-end or unique that not everyone else has, you would get a very different experience from what most people get. So maybe it sounds perfect to you, but super muddy to me.

The idea is generally nice and the rhythmical pattern is good, however, the whole second part feels rather homogenous, I would spice it up with some different riffs. The solo feels a bit out of place. And I suppose there was a struggle in the mastering process. From what I hear the track is drowning in bass, I'd suggest lowering the bass a bit and upping 1-5 kHz instead. Also the drums kind of clip, probably because of the same bass overload. Giving some to 5+ kHz also tends to help make it sound less "closed". Best of luck to you!