Awesome!
Hey, this is my first review so bear with me xD
I friggin love it at 21 seconds especially with the vocal sample thing in the background (Unless im mistaken and there was no vocal sample) either way I liked it haha. I personally think it's a good length too, I seem to recall you saying you like to write repetitive music or something and this is a good balance of repeating loops with some changes and I never really got bored listening through the whole thing. I'm personally not sure about the bass part which comes in at roughly 57 seconds (sorry I can't be more helpful). I think if you're going to write more dubstep you may want to experiment a bit more with the bass part, for example you could make it the focus of the piece and then put in all your background synths/samples and get that deep, subby, wobble bass going perhaps? (although i'm not expert)
Overall I thought this song was wicked! And sorry if i've written too much or not been too helpful (it'll probably be best to just ignore any criticism/ideas I have lol). I think once I finally get my first song approved I'll try and have a go at some dubstep, but I doubt it'll be as good as this :)