I agree with /u/thegraduate about changing the scale. I don't know how much smaller the mountains need to be, but the logo is totally competing with them and it does not need to be the main focus.

I also agree with /u/WhatJewTalkingAbout about adding in an additional visual element that connects the poster more to Seattle somehow. Just make sure that those elements aren't illustrated in a completely separate style from the overall poster.

Shifting the composition down to make the green less dominant would also help. It's not interesting compositionally when the main visual element is right in the middle.

The green mountain is confusing because even with the slight stroke you've got going on, it blends in too much with the green foreground. Perhaps move the blue mountains from the back layer up to the front layer of mountains (especially because they really blend in with the sky), and then have the green mountain in the back row.

Typographically, there's no hierarchy at all. Right now, my first read is Centurylink Field simply because it's the first, but the match name really should be the first read because it's the most important piece of information. Try changing its size, or put it in a different typeface, or use lowercase in the other pieces of text, or any combination of that. Additionally, the line spacing is a little tight, especially because using all caps makes it harder for the eye to make its way through the words, so typically all caps need to be spaced out more than lowercase.

Other random thoughts: have you thought about using texture overlays so that it's not just pure blocks of color? That could add a little depth/interest that I think it's lacking right now.

This isn't a bad start, but I think there's quite a few quick changes that could make it stronger both conceptually and visually. Sorry that this turned into a full on design-school critique. I'm currently procrastinating on doing my own design homework, so I couldn't resist haha.