I was wondering if straight up metal is being posted here from time to time. Glad to see that is the case. Good stuff, sounds fat and tight!
Can't really comment on the mastering. After hearing something long enough everything sounds ok to me mixing-wise.
My humble thoughts on the composition: I feel like the main riffs are being used a bit too much, in the sense of "If everything is cool, nothing is". Under the solos I'd try dialing it back to something simpler so that the riff hits harder when it's coming back. For the intro I would try to create a bit more of a tension arc that ends with the mainriff as payoff, right now it feels a bit like I'm getting to the intense parts too soon. Though that may be part of sub-genre conventions that I'm not too versed with. I mostly listen too other shades of metal.
The lead guitar parts are all cool, but I think I wouldn't start with the harmonized version and save that for the second time around.
Have you thought about developing the main riff into a twice as long and more clearly "different" version of that melodic idea to break up the pacing a bit? You've done something along those lines at 1:36, personally I'd do make that break a bit longer, and I would leave out that short lead guitar sound at 1:36 because it sound to me like I'm about to get a solo (since a new part was marked by the riff), but I'm not getting one.
Just my two cents... You got this, and it's pretty cool already as it is!
My feedback was based on the first dropbox link. Didn't listen to the new one you just posted yet.
By the way, have you ever seen some black metal being posted here? Search came up empty for me.
I'm sure 5+ minutes of non-stop tremolo picking must have many fans around here!