Seasons One and Two were superb. I tried to watch Season Three, but without Claire Foy and the rest of the original cast, I just could not get into it. I feel the producers made a terrible error in replacing Claire -who owned the part of Elizabeth- and think she could have been aged enough with minor cosmetic touches to continue her role.
Looking at the real Elizabeth today, she is still remarkably unlined for her age. If Claire had just a bit of grey added to her hair and a few pounds here and there, she could have maintained the role. Her effortless and nuanced depiction of the Queen just could not be replaced by any actress no matter how talented. I was really looking forward to Season Three, but the cast changes were regrettably too much. I rate the first two seasons as 5-star, and Season 3 as merely average.