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Lets take a scientific approach for this. Assuming you can't logically determine the beauty of the artwork yourself, you need to ask people you know about how good your artwork is.
Tally the amount of people who love your artwork to the amount of people hate your artwork.
I think we both know who wins 
Unfortunately, it's near impossible to have an accurate tally for that, even if you take a specific poll for it. Which I'd never want to do.

It's like asking if people think you're pretty or not. Most people have a hard time answering honestly without feeling like they're hurting your feelings, and I'd feel self absorbed for even asking in the first place.
Meh.
Not being entirely happy with my art gives me motivation to improve my skills so that I will be happy with it someday. I know that I get closer and closer to it all the time, and so for now I am content to just keep working at it.
I'll always love and appreciate the support given to me by my art watchers and commissioners though, even if I don't always share your opinion about my art.
