I thought Whitaker did a good job as the Doctor, especially in this season. I really liked Graham as a companion and Yaz is fine. I find Ryan weak and forgettable, just have a hard time caring about his character. My main gripe is that I just didn't find most of the shows in the past two seasons very good. I did, however, like the last three episode of season 12.
I really like Whittaker in the role. I think Yaz could be a good companion if given more screen time. I have little to no interest in the other two and their relationship. I also think each character is getting starved for screen time by all the others.
I think there were some problematic changes to the role of the Doctor (specifically last season where the Doctor's knowledge and expertise became unreliable -- it's not that the Doctor didn't know something it's that the Doctor knew stuff that was wildly incorrect) and to how the Doctor and crew relate to their environment (all of them wandering around in 21st century clothing in King James' time during a witch scare and absolutely no one commented. Really? The companions used to at least pretend to dress appropriately).