My thoughts on The Dead are over-simplified. I loved the first three albums, and saw them live in ’67, in Golden Gate Park (with The Airplane and Country Joe & The Fish). At that time they were still kind of a Garage/Biker Band, sounding more like they drank beer & wine and ate cross-tops (trucker’s little white pills) than took acid everyday, and that’s what the first album sounds like. Notice the fast tempos?
The 2nd and 3rd album are psychedelic classics, my favorite in the genre. It was when, having become pals with the harmony-singing groups and their members, they made their two Country-Rock albums that their limitations became a problem for me. Not everyone can sing, and singing close harmony is very difficult, particularly live (C, S, & N re-recorded some of their Woodstock vocals in a studio. They were seriously out-of-tune). I just don’t consider Garcia and Weir good enough singers to pull it off: amongst other weaknesses, they both sing flat, and together sound very "sour".
Garcia and Hunter sure wrote some good songs (I performed "Friend Of The Devil", a song I love, in a band), but Garcia and Weir were no Don & Phil Everly or John & Paul. They shoulda stuck to what they were good at. There are pictures of Garcia playing banjo (!) on the grounds of Stanford University in Palo Alto, California, in the early-mid 60’s (playing Folk music; he was of course a huge Bluegrass lover, but was undistinguished at playing it, never progressing beyond beginner level). I never saw him there, but started playing at Frat kegger parties on the campus in the late 60’s. Those Frat boys sure like their beer! They got me drunk for the first time, well below the legal drinking age.
Phil Lesh is a monster bassist, and Garcia has his own guitar style (a notable achievement). Bob Weir is a pretty weak rhythm guitarist (listen to Don Everly, John Lennon, and Buddy Miller to hear how it’s done well), and I’ve never liked the sound of double-drummers. On his own, Bill is, well maybe it’s better I keep my opinion to myself. ;-) Pigpen’s Farfisa organ playing was pure Garage Band, pretty cheezy. His numerous replacements were undistinguished Hammond players, nothing special.
Playing improvised music is dominated by Jazz and Bluegrass musicians, whose skill and abilities far exceed those of Rock (and many Blues) players. Ask one about The Dead, and my opinion of them will seem generous ;-). For those hungry for high-level improvised guitar playing, give a listen to Danny Gatton. He was fluent in Jazz (he cited Les Paul as a major influence), Rockabilly (he worked in Robert Gordon’s band), Hillbilly (he was a master at the Merle Travis style), Bluegrass (he started on banjo), and is a true guitarist’s guitarist. There are a lot of videos of him available for watching on YouTube.