‘The WebForms Rant’ by karl Seguin

"ASP.NET WebForms is an ugly and messy framework that complicates an otherwise simple thing. ViewState, codebehind, postback, page lifecycle and databinding are things that you have to constantly program against."
"A framework that accepts that HTTP is stateless will always be simpler, cleaner and more powerful that a framework that doesn't."

Wow! Well done :)
I agree completely. Karl probably is a first developer whom I highly respect (as my virtual teacher too) and who is stating the matter straight and without usual 'polites'.

One more important argument against WebForms is that it leads to hard-to-avoid "Web page was expired" problem due to inability to implement Post-Redirect-Get (PRG) pattern.
See http://pro-thoughts.blogspot.com/2009/06/classic-aspnet-improper-abstractions.html

I also really like a classic I Spose I’ll Just Say It: You Should Learn MVC article by Rob Conrey.
Finally, recent MVC or WebForms: It's more about client side vs server side article by Ian Cooper is good too.

Don’t forget to read comments under all those articles!