Fair points. I personally judge a song on its composition rather than its mixing, and as many songs don't have perfect composition at this point, it's hard for me to rate a song as even 8-9 (at this point). I prefer being a hard judge, because as somebody said in a response, everybody needs a slap in the wrist every once in a while. I plan on giving that. If the track truly doesn't have anything wrong with it, and the composition is well done, then THAT gets a 10 from me, the mixing (as long as that doesn't hurt my ears from being too high-pitched/staticky/distorted) doesn't matter that much. Remixes and arrangements rarely ever get more than a 7 from me, as they lack much originality (unless the remix takes it and brings it out by a huge amount). Re-instrumenting it isn't that impressive. It shows that yes, you can listen to a song and tell what the notes are. That's about it.
So, I guess my system is...
10: Absolutely perfect. Composition is formatted well, there's nothing wrong with the mixing that I can tell, it sounds cool and interesting... I have no complaints about this.
9: Needs a bit of polishing, maybe the mixing is incredible and has some interesting bits, but the formatting isn't quite that good, or there's some distortion, or something!
8: Not all that well composed, has some things off-key that don't work, not fully formed ideas...
7: Eh. Some cool effects. Not well composed, not particularly interesting.
6: Generic. I've heard all of this before except the tune, everything else is just formatting and effects that are basic.
I think you can figure out the progressing of the rest of the list from that.
