There seems to be a general consensus among webcomic creators that they should be receptive to criticism and use it to improve their work. I don't agree with that mentality. I'm arrogant and self-righteous, and I don't think anyone else knows what I'm trying to achieve with my webcomic better than I do. And I know just how flawed my artwork is and make a conscious choice about whether to take the time to do it better. I never ask anyone for criticism on the content of the comic itself, and I never expect it, unless there's some blatant error in the text. My mentality is that my comic is all my own, and those who enjoy it will stick around and love it for who it is, and those who don't like it will move on.
While some people think they could benefit from criticism, I think it would drown my inspiration if I paid attention to it. If I get into the mindset, while writing, of thinking about what other people think, and what they're expecting, I can't write with the spontaneity that I originally intended for the life of the comic. I do the best writing when things don't turn out the way I, or anyone else, expected them to.
Although I don't like people leaving critical comments on my website itself, I do approve of critical reviews written on other people's blogs or websites. A review is different from direct criticism because you're talking to your audience, telling them how the comic may be received, and whether it's good by certain standards - you're not talking to the author, telling them how they should make their comic different. The former thing seems presumptuous and even rude to me if the author never asked for criticism.