Brains in numbers are of course, an asset. But what if you're a one-man-army in the VOCALOID scene?
This puts you in a rather tight handicap.
In any form of art, one's creator are oblivious to the flaws of his/her works at the time of production.
This means there may be flaws that can go unnoticed by the creator, but not by other sets of eyes, brains, and such.
I was taught in a scriptwriting seminar, that to be able to self-critique, as soon as you are done with the piece, leave it as it is for 3-5 or 7 days and forget all about it (forget everything but the fact that it exists). Then come back to it and look for flaws.
This is a really bad proposition if you are under time pressure, or if you are keeping a schedule.
Typically, I'd take a week or two going over any musical piece I'd make/cover and work on it closely with other people, or listening to it keenly until I find no more things to tweak.
Is it me, or was my choice in using Luka the failing factor? There are people who think Luka is detuned in the piece in comparison to the original(s). But there were others who think she did good.
Whatever it is, I have encountered cases of Luka detuning long before I worked on her, so this is worrisome to me.
The source MIDI file could be a problem too, who knows what kind of SYSex it had that may have caused it?