I've seen all of them except for the latest and last, The Wind Rises.
And I just realized that their order of release almost exactly matches how I'd rank them. The Castle of Cagliostro was good but not great, which is understandable since it was his first and he was just following the TV series. Then came his sophomore masterpiece, Nausicaä, which was based on his own epic manga. But it's been a steady decline ever since. Sure, everything was still great through Princess Mononoke, just less great with each successive one.
Things really started to drop off with Spirited Away…