My girlfriend read them and loved them. She loved them so much that she read them again. I read the last one so she could have someone to talk to about it and it wasn't my cup of tea; I'm not going to bash my girlfriend over the head though for enjoying it.
I enjoy Stephen King, George R.R. Martin, Lovecraft, Hemingway, and many others. I read a lot. I've read books far, far, far superior to Twilight. But people enjoy them; they're fun. The prose is far from perfect, the descriptions are dull and childish sounding, but people enjoy them.
I don't criticize people who say Stephen King doesn't write literature, only garbage. They're entitled to their opinion; as am I.