I am here to say that 40 years of crowds have been wise to revere this show. It kills. Let me just mark a few points, but urge you to check it out yourself, perhaps especially from shnid-138677, which sparkles.
First, I guess Johnny D and Jerry just needed a little work together --they hadn't played since 11/18, and I doubt they had practiced between time. Yes, I'm talkin' 'bout practice. So we see monotonic improvement in how these two are sync'd, and that makes everything else work. By 12/21, I do not notice any problems at all - not a one. And I hear Johnny D doing some killer stuff, e.g., in Sugaree, that validates why Garcia wanted him in the band. He's really, really good.
Second, Ozzie Ahlers plays masterfully here, going toe to toe with Garcia with tremendous confidence. This would be less and less the case over the years of Garcia's side bands - Melvin Seals was wonderful, a perfect complementary player who could take sparkling features when it was his turn, but was certainly very submissive vis a vis Garcia. Here, Ozzie occasionally steps forward over Jerry, Jerry keeps playing loudly, and, rather than backing down, Ozzie ups his attack and amplitude. They really feed off each other wonderfully this night. Nick pointed out to me that there is no synth here, just electric piano, so maybe that gives his playing a little more oomph or something, I dunno. Or, like Johnny D, having played a few gigs has him feeling warmed up. Or, it's just a great night. Whatever the case, a great night for Ozzie Ahlers, the best I can recall having heard.
Third, Garcia plays very mathematically throughout, and alternates between loud, grungy rock and roll lead guitar on the one hand and some much more gentle, patient plucking on the other. I can't explain why it feels mathematical except that it's both arithmetic (like an expanding cycle) and geometric (lots of loop and circles). He also comps as well this night for Ozzie as he ever did. See especially "After Midnight", which rocks hard.
Fourth this "Positively 4th Street" more than earns its reputation as the BOAT version. Checking in at 17 minutes, it starts with some beautiful instrumental work, as Jerry patiently sets everything up. I wasn't following along with the lyrics or anything, but I think he gets all of the verses almost entirely right, and sometimes he just barely remembers a line in time but offers it up off the beat and a little faster, providing some really nice syncopated texture. I think he even has the verse order mostly right. His guitar tone works throughout, and he comps aggressively for Ozzie, including some fanning that would normally just be him but here serves the whole unit. By the end I just wrote "I am actually pretty speechless at this point. WOW." Check it out.
Fifth, I seriously doubt that HTC was really an encore. In this period, a 35 minute second set would only have happened if they were running up on closing time. But then they would not have been able to play an encore. So I suspect it's just a four-song, 50-minute second set.
Sixth, I also seriously doubt that this comes from master reels. Maybe I shouldn't - the tape sounds absolutely fabulous, and it sounds even better, on a quick comparison, via shnid-138677, than the "Bertha" version I got with. It sounds light years better than the cassette master of the next night, which doesn't circulate but which I have heard. But all of that said, I am just not aware of anyone running reels at this point. The last Garcia Band reels I know about date from summer 1978. Betty ran reels for Reconstruction at least into July 1979, but the Garcia Band tapes from after that were limited to cassette. I dunno. It seems pretty certain there is a cassette gen here, based on cuts in After Midnight and Harder They Come. Older circulating versions have also tended to be a little bit hissy. But, I dunno. Happy to be proven wrong!
So let me just close this fun little exploration that I do think 12/17/79 was quite weak, but the band gets better each night of the three I have engaged over the last few days. The 12/21/79 show is absolutely outstanding, holding its own next to anything JGB did plus or minus a few years. I have seen folks say that they use it to introduce novices to the Garcia Band, and I can see why - the tape sounds great and the performance is outstanding. True, I can hear the limitations creeping in to Jerry's voice, which is still sweetly high but which is starting to bump into tighter range and volume constraints. It ain't perfect, but it is excellent.
Listening notes below the fold.