it's always hard to tell what was lennon and what was george for me. he improved in the later years, his work on strawberry fields was great for example
he was okay, i am more of a fan of his lyrics

a sad thing was that he was using the same chords
a good thing was that he wasusing the same chords but he used it in a advanced way
I think he was good, his riff on Get Back is cool, and across the universe and julia have nice guitar parts by him.
I really liked Lennon's acoustic fingerpicking style that he always had but perfected in India. The early takes of SFF comes to mind and also a number of solo demos such as #9 Dream, it was nice to hear that song stripped back to vocal and his acoustic guitar.

As for his rhythm guitar playing in the early beatles where you can hear it at its most pronounced because it is the loudest, he turned his amp up the loudest.