I've just finished watching Time and the Rani, McCoy's first story. It's pretty mediocre. The regeneration is complicated by Colin Baker not returning and being subsumed into an amnesia plot thread, which leads to an awkward scene of the Doctor and Mel trying to prove who they are to each other. The defining character trait of the 7th Doctor here is muddled idioms, which is incredibly annoying. I'm glad that didn't stick around. Say what you will about McCoy, but he had frantic running down pat right from the off.
I'm watching the special features now and there's a scan of Sydney Newman's ideas about how to improve the show from during Trial. His new companions are hilarious:
And we'll never know what he is, but it cuts out there.