I'll have to buck the trend. I thought that episode was dreadful. It's like they are flat out of ideas and the 'monster of the week' was basically just a big round firey ball.
Saru for me is the best character by a mile so it was good he got a decent story for his own character. The rest, the Tilly stuff, the main story, the whole engineering bit was just so dull and poorly written in my opinion.