Re: What are the core and best episodes?
I would probably uprate "Shuttlepod One" to a must see. It's one of the best episodes of the first season and it's the start of the Malcom and Trip friendship. I would also downgrade "Vox Sola" from must to see, to recommended. I find it a decent enough episode, but hardly a must see.
On the continent of wild endeavour in the mountains of solace and solitude there stood the citadel of the time lords, the oldest and most mighty race in the universe looking down on the galaxies below sworn never to interfere only to watch.