I'm very critical of my own beer. I generally know when something I make is really good, and my competition scores generally seem to bear that out.
When other people (generally non-brewers) try my stuff, even what's not quite up to my high standards, they generally don't notice the flaws that are so obvious to me. It's only rarely that somebody points out something that I didn't notice.
I think it's definitely the curse of the artist - I know what I was shooting for, so if I don't hit the mark, I'm acutely aware of it. Other people don't have that same expectation, so are much more open to enjoying something that isn't quite spot on.
I will say, though, that much of what I make is better than most commercial beers. My brother, who does have an excellent palate (although not yet the vocabulary to describe things) agrees - he's one of the few non-brewers I know who can pinpoint the off flavors that I pick up in my own brew.