Nurse Betty has that odd but winning combination of a repellent, unease-inducing plot with extraordinary characters. In the same way I loathed Fargo on first viewing, then realized I was still thinking about it days later and enjoying it somehow, I liked Nurse Betty a lot more the day after I saw it. Hard to understand, harder to explain. As others have said, it's quite forced in many ways, but that seems to be part of what makes it so striking.
Fair job by Greg Kinnear, great work from Morgan Freeman (although I worry that he's being stereotyped as the principled villain). Chris Rock was good but not a standout. Rene Z. is so natural it's unnerving -- i.e., unnerving to be "natural" playing someone not well in the head. Also liked the sort of "abrasive sparkle" performance from Allison Janney in a small part.
Don't go expecting as much of a "road movie" as you might assume from some synopses. (There is "road," but it's only barely relevant.) Rated 8/10.