Don't take this as insult, just telling my opinion possibly an advice.
The top banner is prettty solid but the other (lower) part is kind of bad to be honest. Maybe it's just your style but i would suggest you watching some "flat-style long shadow" tutorials to improve stuff like that horrible drop shadow at the designs/videos windows. I like the idea of the buttons, although the text is pretty widely stretched. I would stretch it a bit horizontally so it won't look so unnatural.
Few pretty decent flat style tutorials (i would still suggest making a bit more research)
http://fltdsgn.com/page/2/ <--- this site is a collection of other sites with pretty decent designs, you can get inspiration from :)
https://www.youtube.com/watch?v=AnvqL1yg9X0 (https://www.youtube.com/watch?v=AnvqL1yg9X0)
https://www.youtube.com/watch?v=AWhnbTQFk0E (https://www.youtube.com/watch?v=AWhnbTQFk0E)
For the picture
Also nice attemp with the picture (I'm assuming it's selft drawn). Recently I found out about this easy new technique. It's what I call "low polygon pictures" It's great because you don't need a drawing tablet to get impressive results. Here are some previews:
(http://s25.postimg.org/732fgn167/Untitled_2.png)
That's all. Hope I helped, sorry if this insulted you!
~ SickzMedia