Prince is technically fantastic, from any musical standpoint.
His new album is really, really good, as well. His "dual" album with Third Eye Girl - not so much. The SNL Performance was around half and half and not the best showcase of either, although a great showcase of instrumentation.
He became a witness because he was distraught over a death, and Larry Graham showed up at exactly the right time with the right message. His songs went super-witness for a while, now he's normalizing back into his old style again with the latest albums, with only a couple of songs referencing Witness type stuff in the lyrics.
He was always eccentric, but most geniuses are, especially when they can get away with it (which he can).