I can understand your apprehension, although you forget one thing: as a musician, I get too "close" too a song to hear it with fresh ears. I can notice, and correct, small details and mistakes. However, I don't have the opportunity to hear it for the first time.
I am a writer on top of being a musician, and constructive criticism is the best thing for a writer's work. I would not only like my song to be critiqued, but the lyrics also. If not especially. Songs are about being able to get lyrics across acoustically.

Anyway, please do critique my song, my lyrics, my voice, my life--anything that you think would help make me better as a musician.

Thanks,
Zack