Til you need to be diagnosed with something. I'm avoiding Kaiser at all costs. Ever since it took them a year to diagnose my rheumatoid arthritis after I was presenting with literally textbook classic symptoms I haven't trusted them as far as I can spit. Friends in the medical field around here have told me they avoid working for Kaiser so they don't have to have it as their medical plan. They're good for treatment but really really crappy at diagnosis.
I have physician friends that actually love working for Kaiser, but basically: YMMV.
I think the main issue with Kaiser is that they are phenomenal for general care, but they do suffer from issues regarding chronic illnesses. The MO that I get about them is that by and large, it is a great model and a very good system, but not very good for dealing with nasty cancers and such.
That is, indeed, a legit criticism. It seems to be an issue with other systems, as well. My brother was a physician at Stanford Hospital and the policy among physicians there was to get insurance through PAMF, which offers great family care and great costs--but again suffers when it comes to diagnosing and treating serious illness. That was all well and good until he got the butt cancer, his treatment basically sucked for that year (nothing akin to malpractice or anything--just that they lacked resources which, fortunately for him knowing everyone in the country he needed to know, he could get elsewhere, but there were still delays due to information and traveling, what PAMF could actually allow, etc) and we do tend to feel he would have been better served if being treated through Stanford. Honestly, nothing would have saved him in terms of initial diagnosis and the treatment paths chosen after conferring with all sorts of people at each stage, but there was a lot of unnecessary frustration involved simply because he had to go "out of network" so frequently.
Mayo clinic is similar, and probably better than Kaiser. I have family that work for them, as well, and one thing they definitely handle properly is diagnosis.