Most criticism I've seen addresses protagonist Andy's (Ian Nelson) weak characterization, and the show's unimpressive attempts at connecting fictional plot with the real world. I'd argue, though, that the writers are not entirely at fault; the show's premise and setup are inherent transgressions of the modern television show formula. Between the fact that we, as the audience, don't get to spend much time with the characters on screen (about 3 hours), and that Andy resembles nothing of any modern protagonist, critics have labeled Andy an unsucessful attempt at creating a believable protagonist. In truth, creator Paul Reiser took a risk in introducing an unconventional protagonist by today's standards (conventional in 1970) to really enhance the show's nostalgic qualities. Most viewers of on-demand streaming services like its network Hulu and its original network, what is now the defunct debacle that is Seeso, are too young to feel nostalgic for something they never experienced. Most contemporary period dramas like AMC's Mad Men feature anachronistic modern characters. Andy is very much a 70s character in a 70s setting, and not a modern character in a 70s setting. Naturally, then, the show's attempts at linking Andy with the real world fail, because the viewer simply can't relate with Andy. Still, I think it's refreshing to see a change, for once, in a television era dominated by dark, jaded, and overly pessimistic protagonists.
On the opposite end, Jane Levy's fantastic portrayal of Joy Greenfield features a very modern character dealing with very modern issues. When Joy is on the screen, There's...Johnny is at its best. The show does a pretty good job with the writing as a whole, but Joy's story arcs and relationships are especially captivating. It's really a shame she doesn't receive more screen time.
Other than that, the show is competently directed, well written, and wonderfully performed (especially Jane Levy and Tony Danza). It's really unfortunate that, with Seeso's untimely demise, There's...Johnny doesn't get the attention it deserves. For a show with only roughly 3 hours of runtime, I'd definitely recommend There's...Johnny for an afternoon binge watch.