I gave it an 8, but I was probably being a bit generous. Definitely some good parts to it. Great to see the Master back with one of his classic plans. Work with aliens towards an evil end with the ultimate goal of double-crossing them! Classic! Of course, it all goes wrong. Also classic.
The concept for the aliens was interesting. From another universe, beyond even the Doctor's technology to understand, able to break into the TARDIS! Exciting stuff. But, they were fairly dull onscreen. I suppose, as the Doctor explained, they weren't as stable in our universe as they would have wanted. Kind of explains about how they were so powerful yet, at the same time, kind of ineffective. Just glowing light that would appear.
The escape from the plane was fun but, if they open the Bill & Ted method of solving problems, where does that end?!
Like the first part, this episode tried to be action oriented but ended up being very talky.
I did not like the destruction of the Gallifrey by the Master. We just saved the darn place. I'm also very leery about Chibnall recasting Gallifrey lore. Doing that in an interesting manner is a tall order, and I just don't trust Chibnall's story telling abilities at this point.
Total speculation on my part, but I'm guessing that the finale will reveal the new origins of Time Lords to be connected to humans/Earth. That we evolve into them, maybe over millions of years, and thereby explaining how humans and Time Lords look the same. Also, a subconscious knowledge of that connection would explain the Doctor's fondness for protecting Earth.