Discussed at length here.
To answer your questions, I think he's definitely one of the greats of guitar in general, and certainly a very versatile musician. He's been a major influence in my approach to music and the guitar, though lately I haven't been listening to him much. My favorite albums, in no particular order, are
Question & Answer, Bright Size Life, Rejoicing, First Circle, Live in Europe, Secret Story, Missouri Sky; and the sideman stuff with Brecker, Gary Thomas, Sco, and J. Redman contained some excellent music, too. I didn't think he was a great match with Garrett, personally. I'm looking forward to the new one; I thought the last Group album/tour was the best in many years.
The only "weird" project I've listened to at length was Song X. I do hear it, and I like it.
I'm not going to touch the overrated/underrated question.