The Times's Matthew Collings dismisses Banksy's art, writing that his "ideas only have the value of a joke." I responded, rather tartly, in the comments:
In order to make his case here, Collings presents us with a fallacy of limited options: Banksy either has to be Rembrandt or he's rubbish. On the other hand we have exceptional cartoonists and illustrators who create inspiring work every day and who don't claim to be anything "higher" than their occupation. Banksy creates simple, striking work, which often provides concise and scathing criticism of authoritarian government, surveillance society, and war. I imagine, to some extent, it may be your conservative sensibilities Banksy has offended, more than your sense of aesthetics. So be it.
I should add that he also often satirizes capitalism and consumerism, which I'm sure does little to put him in the good graces of a conservative paper like The Times.
Check out this BBC News story about Banksy's work in Bethlehem, Israel and the Palestinian/Israeli wall. Also, this NPR story by Erik Westervelt about work by Banksy and other guerrilla graffiti artists in the same area.