I give everyone at least a five. I would say there were no "bad" performances. They were mostly reinterpreted covers (except for Paul and Ringo's bits, of course), and as such should not be expected to match up to the originals.
I don't really get people crabbing on Maroon 5. I'm no particular fan, but they played the right notes on their instruments and were on key vocally and did the right harmonies. Maybe a bit low key energy-wise, but that would be my only criticism.
Katy Perry's contribution has been overly-vilified as well, I'd say. Altering lyrics to change the gender is a timeless practice, and her performance was fine.
The other younger artists did OK too, imo.
I was somewhat disappointed with Annie Lennox's vocal performance. Sounded strained and tired. Might have just been an off night for her. But still a very touching rendition of the song.
I agree that 'Something', 'Hey Bulldog', and 'WMGGW' were highlights.
And yes, I would say that 'Hey Jude' gets trotted out as the big finale a bit too often. There were other good choices that could have been made.
In all, there were a lot of moving moments for me and it was an entertaining show. Glad they did it.