I didn't feel it was as bad as some of the comments here seem to indicate. I would give them a lot of marks simply for the effort to begin with and considering that it is simply a labour of love (as many of these videos here seem to be), it is very well done indeed.

kind of makes you realize how bad the actual music with when it is played orchestrally.

It depends, it can also just be a crappy adaptation. I personally like this piano version: http://www.youtube.com/watch?v=jd-h0debytI&list=UUl3iv3e...

What stingraycharles said. It depends on the adaptions. I liked this one by the Ohio marching band 110 Gangnam style

http://www.youtube.com/watch?v=cDficEfonAE

It makes you realize how bad the synthesized instruments they used for it were... also not arranged for an orchestra. You can't just simply take the original note for note and play it on different instruments.