I read Valis a month or two back and I find I've already largely forgotten it. A test of good writing- in fact of good art in any medium- is that it leaves you with unexpungeable images in your head.
Dick wrote Scanner in the 70s and set it in the 90s. It feels dated. And all the predictive stuff is wrong- of course. Basically its an everyday story of brain-fried hippies with some portentous, paranoid sci-fi stuff tacked on.
He can't do character. All his people are interchangeable. And when he's writing about women he notices whether or not they're wearing bras under their tight sweaters and that's about it. He goes on and on about how boring druggies are and- yes, well- he's right.