Whittaker was almost there, but didn't quite nail it for me. Very much felt like a performance, almost a throwback to the pre-reboot Doctors, and not in an especially good way. Overall plot wasn't terrible, but the script wasn't especially well written or clever either (setting up a deux ex machina off screen, bleh). I appreciate really emphasising the danger they're all in by actually killing the supporting cast, but the way they telegraphed it all diminished its impact significantly. Companions seem. . . sufficient. Introducing three of them all at once was always going to make the job tougher than it needed to be, but I can name a dozen guest stars over the last few years who left more of a lasting impact.
Overall, it feels like there's a lot of potential. I'm hopeful, but I won't be making an appointment to watch it live if the next few episodes aren't a solid step up.