I thought the strong lead was Lauren Graham, but saw the other three as weaker. As a viewer, I want to see Nathan played by a more charming & handsome man. (Hard to beat Frank Sinatra). I didn't feel compelled by Kate Grant either. (But, likewise, it is hard not to make comparisons with Jean Simmons. Same problem finding someone as strong of a lead as Marlin Brando.)
However, I loved what Lauren Graham did with her role, and I thought ALL the rest of the cast was amazing. So fun to watch act and dance and so fun to listen to the songs! Overall, I really enjoyed the show and thought it well worth the price of admission.