Basses are sidechained to a silent kick (a first for me), but you are right about the sustain. I was already looking into the releases of the bass and some of the synth stabs.
Since I'm still learning to listen and mix, care to point out some specific problems or example? That'd be really helpful!
About the lead guitar... I'm not sure if I can get it much better than this. Maybe it was a dumb idea anyway, I'm considering replacing it with a screaming synth. Would also fit the song and style better. The other option would be to get a real guitar recording, but that might take a while.
Lastly, your remark about source usage has me kinda worried. The only real original parts are the speech part and the wobbly bass part, the other parts are either the original (2 loops of about 40 seconds) or beavily based on it (the intro and outro). Still, the song is 4 minutes, of which about 80 seconds clearly source material...
Awell, maybe it should just be a nice song to listen to in stead of my first OCR submission if that's a reason for rejection