Furthur has a way of sucking people onto the bus, willing or otherwise
There was a great interview I think by Jackson on dead.net (?) of JK that was very interesting. He hasn't spent his life copying Garcia. In fact, he makes an interesting comment that unlike a lot of people who play guitar because of the dead, he was already an accomplished violinist and guitar player until he, too, was thrown on the bus. So his background is not copying Garcia. I can't blame him for wanting to play Garcia great. If we are that critical of guitar players, Jimmy Page sucks becaus he played Jimmy Reed note by note in everything he did.
I look at it this way: He plays Garcia the way it should be played- on China Cat, you get the riff the lead should be playing for it to be authentic, on Deal, etc. For all teh other dead incarnations, it seemed the guitar players said, "oh, key of E, I can do that..." But to play lead on Grateful Dead is more than that. On songs like Let It Grow, Music Never Stopped, and the like, where there are those moments where the lead better be in that spot to grab it and throw the music into the atmoshpere - or the song collapses, JK is faithfully there. Where the song goes into (even somewhat) jam or improv, John stays true to the feeling of the song but takes it his own way. I think the one thing he does copy, and I really heard it on this past NYE, is the expressive tones from the electric guitar. It's very nuanced but it really adds a ton of depth to the lead guitar. I don't know what it is, but I like it. I personally think Garcia came with that sound in/around 1981 and I just love it.
I wish I was 20 again and not married and bills. I'd quit my job and go on tour like it was 1988 all over agiain. Don't let preconceived notions of the past prevent you from experiencing the grateful dead experience in all its glory.