Depends on how well a judge knows the genre in question. I'm generally more comfortable critiquing jazz and solo piano arrangements than say, Tibetan throat singing. The less I know about a genre, the more general I have to be with my criticism.
I'd estimate that I like about 70% of the stuff I YES, and maybe 10% of the stuff I NO. There have been a few heart breakers for me, definitely.
Probably my biggest pet peeve is when first time submitters write a fuggin' novel about the remix they threw together in FL in 6 hours. They write 4 paragraphs about playing the game for the first time at age 7. They mention the names of everyone who listened to earlier drafts. They thank God, and their parents. And after all of this they suck profusely. There's nothing that calls down the fire (as far as my votes are concerned) like a longass pretentious submission email.
Once you get a mix or two posted, feel free to write a ton, as Dave likes putting that stuff in the writeups. I do it all the time.