Beginning sounds nice. Well used percussion, but it's kind of repetitive and old-school.
Build-up sounds really good, it just needs white noise xd
Drop is catchy, but not that dubstepy, but you still did good job on it. You could also make it a little bit longer :p
I also noticed a little sound glitch on the beginnings of build-ups.
Overall: 4.5 stars.
You just need to work more on those dubstep sounds xd