It's not serious, not pretty. I know nothing about design, but I don't like it. Look at Flask, for example: http://flask.pocoo.org/, it's simple, but seems much more serious.
I've read more about it and your framework and it really seems very very nice. That CLI thing is great, but the landing page is really hurting adoption, I think.
If you have anytime, I've made some modifications and I'm curious what you think? http://www.hug.rest/
I appreciate the feedback, and I think your probably right. I'll go back to the drawing board a bit and see how I can make it look more serious and professional, while not quite as boring and plain as the Flask page.