While they may not have been at their absolute best, they have been much worse, LOL! To me personally, the Pig Pen era was their finest hour. At the time of the movie, they were pretty much burned-out from ten years of grueling touring and were at odds with Mickey over financial issues. Keith was a decent (if inconsistent) player , but Donna was mostly caterwalling, LOL! Still, the relatively youthful Dead does a decent job, short-handed or not.
Personally, I think the Dead made a good choice in replacing the Godchaux's with Brent Mydland..he sang better than Donna, could do a decent male lead voice and was a decent on the keys.
The movie bonus disc stuff is particularly nice...with a promise of more things to come from Dead A/V Archivist David Lemieux.