I don't think they are a joke band- their second album, 'One Way Ticket To Hell and Back' was terrific, imo. Far more ambitious in every respect than their debut, with well written, flamboyant rock tunes. There are some songs on there that can, and probably will, stand tall with the rock greats a few years later. 'Seemed Like A Good Idea At The Time' is one of the all time great rock ballads imo, 'Dinner Lady Arms' is not far behind the quality of Queen, and 'Girl With The Hazel Eyes' and 'English Country Garden' are pretty damned perfect. The one misstep on the album is the overtly twee 'Girlfriend', a real cornball imo, but the rest is great. One of the best rock albums I've heard in absolutely ages.
I think it's a bit much to chastise them for being a joke for having humour in their songs- Queen, The Sweet and Sparks, for example, are roundly praised for the same characteristics- to sl*g off The Darkness for this smacks of double standards to me personally.