Needs More Content and Style
Honestly, this shows exactly how Newgrounds rating system is flawed. If someone spend 20+ hours making a mediocre game or animation, with sound controls, fully unique, and with original code and/or art, it should get a higher score than this.
That being said, this soundboard is functional, though other than utter novelity, it's nothing special. It has no graphic appeal, really. In the future, I would make sure to use some high quality images that really complement the overall style you are going for. And this doesn't have that many sounds either. I think that I would actually use this more if you included all of GIR's key catch-phrases, and viewer's favorite quotes. I liked some of them, but others were not as funny. All in all, a decent final product.
3.0 out of 10.0, just because I like Invader Zim, and there was definitive effort in the creation of this board.