Thoughts on a couple of mixes? Death Metal and Metalcore.

Hi!
The metalcore song have too quiet drums, but the guitars are dominating (you're guitarist, right?). The guitars sound noisy a bit (due to quad-track probably?). And the bass has a good sub-range basement, but no audiable definition (mids and hi-mids).
I'd recommend processing the drums first, to make them punchier and more powerful.
The guitars may also have less 2-3k in their tone, IMO. :)

Pretty the same as for the death metal mix, except the processing and the tones might be different due to the style differences.