I've never been a Deadhead
Q: "What did the Deadhead say when the drugs wore off?"A: "This band sucks!"
If you told that joke three decades ago, you were most likely being ironic. Today, chances are you're simply repeating something that you think is supposed to be funny, without really understanding why.
I've never been a Deadhead. To me, that's a cultural experience that formed around the musical and artistic vision created by the Grateful Dead.
I liked a lot of what the Grateful Dead did in the late `60s and early `70s, both in the studio and in live performance. It's absolutely true that they weren't firing on all cylinders all the time. I've been to shows where I wondered why I even bothered going. When the Grateful Dead were bad, they were ... forgettable. A few years ago I tried wading through a bunch of archive recordings I found on the `net, confirming my recollection that one must wade through a lot of mediocre material to find the gems.
The reason I stuck with the Grateful Dead (for a few years, anyhow) is because the inspired moments were - without exaggeration - transcendent. And not just by comparison to the bulk of their show.
The Grateful Dead embraced a different aesthetic. Experimentation and risk-taking were obviously more important than polish and consistency. If the Grateful Dead were some obscure band that never made it outside of their hometown I'd say "good for them, sticking to their principles." But the Grateful Dead were one of the most (perhaps even the most) financially successful act of their time. In other words, they had a lot of fans who were willing to indulge and support the Grateful Dead's musical aesthetic.
I'm one of those people who believes that music should be more of an art form and less of a product. I don't believe that a musical artist should create with the intent of selling something. The expectation that art fails unless it becomes a successful product is a fairly recent (in historical terms) development that says more about capitalist culture than about art or music. I think it's exciting that the Grateful Dead experimented so freely and found support for their music. I think it's a lot less exciting that some pop performer can fill stadiums at $100 per seat and put on a highly produced, choreographed and sequenced, no-room-for-error stage show. The former is art; the latter is merchandising.
Anyhow, the point is that you shouldn't judge all music by the same criteria. You wouldn't compare Beethoven to Elvis or Charlie Parker to Brittney Spears. The Grateful Dead inhabited their own space. Love them or hate them: that's your right. But at least try to be aware of what they were trying to do rather than hating them just because they don't validate your own musical preferences and prejudices.