Check your levels -- there's a lot of peaking going on here, even with what sounds like master limiting compression.
Also, 6 minutes is pretty ambitious for a dubstep piece. You could probably stand to cut or move around some sections. Like at 3 minutes, I swore we were going into a drop -- but this is a build/breakdown. Put that section before a final drop. The one before it is a good build. Looking at your waveform alone I would have expected 3:00 at like 4:33.
Mix wise, that low portamento synth I would say is a little too loud. Take it down maybe a dB or so.
If you're mixing with the mastering channel FX on, don't do that. It's basically impossible to mix well like that. Turn your mix volume down to like -6 dB, and then mix all the tracks as sounds good to you there. You'll find you make better mixing decisions when the loudness factor isn't there to make things sound cool. I'm really prone to this myself so I understand. When you're done, turn it back up! If you have a mastering service you use, mix the track down at say -6 dB and then send it to wherever you plan to have it mastered.
The phrasing you have with Dubstep bass for 3 bars, then 4th bar of instrumental after being repeated 4 times per section gets kind of old. Try some variation of rhythm even.
I do like the thrumming bass at 3:36, but I feel like it doesn't really get enough presence in the mix. When mixing, also, resist turning every part up when you want to hear it. Instead, bring down whatever you think is in the way. It goes a long way and makes the end compression sound better.
Buildup at 4:21 was really unexpected. I feel like that spot without the percussion could have been dropped -- or the OH WOW could have been a quick two shot like you have in your crazy outro. Really there are so many buildups here without a lot of change to the drop or opportunity to get going. I would space them out a lot more. As is it makes the song sound like it doesn't know where it's going.
A typical dubstep structure will help you here. There are plenty of templates online. Take one you like, mark the drops, builds, and intros or outros, starts of the risers, and then delete the rest of the template. Work on that structure as your base, until you get a natural feel for song structure. It will help you a lot.
Mix wise the biggest thing I noticed was clipping/peaking and a lot of clutter with reverb or instruments with sustains kind of just being put to the side chain without thinking about how sound bleed works.
Reverb, always remember less is more, and make sure there is a ton of low cut on your reverb, at least up to 250 hz. These frequencies make an instrument sound boxy. Try to keep a low wet signal with a fast release. If you really want that big slap back or long tail sound, try a delay, also with low cut and quick release time. Ping-pong makes all the difference. I will even admit to abusing it.
EQ wise on each instrument that is not your bass I would cut the frequencies below 250 hz. You may think they sound tinny solo, but in an ensemble, these frequencies get very loud and stand in the way of your bass, kick, and snare. Too much of them even and you can just end up with a headache. It will sound like a swath of pink noise in your track. I hear a lot of that here, mostly reverb but still.
Also, I would not compress your track as hard as you are now. It makes it feel like it doesn't really have a pulse or depth, even with sidechain there to give the impression of oomphing kick and DSH snare -- speaking of, gated reverb is a sound to look into for your snare to get a little more mileage out of it. Look that up. It's a great concept that can be used on any instrument.
Anyway, enjoyed the track. Moving it to dubstep. Thanks for coming out to NGUAC!