Well Kublakhan, luckily for me I gave the Dead a second try, or else I would have called you a liar!
My first experience at a Dead concert was one of the worst concert experiences of my life. It was dull, boring and the accoustics were terrible. (I saw them at one of their New Years shows (albeit a Chinese New Years show in Oakland), many, many years ago. The set list stunk, (unbelieveably, the best song they played was Alley Oop), and their playing was uninspired.
Luckily, I caught them a few years later when they backed up Bob Dylan for one of the Days on the Green type of Concerts in the Oakland Collesium. They seemed like a totalling different band. Energized, rockin' and just having a good time. (And the set list was great, not a bunch of obscure songs from their lessor albums and B sides.)
As far as live performances that exceeded my expectations:
Nils Lofgren, (I had never heard of this guy, and he played at a Bridge concert and blew me away!)
Stone Temple Pilots,
Kronos Quartet
Those that dissappointed me included:
Jethro Tull, once anyway. (And like the Dead, a second concert impressed me as to how good they could be, given the chance).
Smashing Pumpkins (Twice they stunk! Never again for me!)
My two cents worth anyway.
