Just recently rewatched this 6 part serialization of the Narnia story The Silver Chair, and enjoyed it immensely, due largely of course to Tom's wonderful performance as Puddleglum. I'd forgotten how good he is in this, and it's also probably his first big 'comeback' role after leaving Dr Who (after his admitted failure as Sherlock Holmes), having been all but absent from our screens for the best part of a decade. Tom seems to have really relished his character here, and is wonderfully likeable despite playing a 'gloomy' character - in fact the more miserable Puddleglum becomes the funnier he seems! The scene where he gets drunk is really funny, but he also gets some very powerful scenes, especially at the end where it's actually Puddleglum who saves the day (like the Doctor!) and has an impressive speech that Tom delivers magnificently. I'm sure alot of the filming must have reminded Tom of doing Doctor Who as it was a BBC production with a fantasy theme, special effects some very Doctor Who-y sets, and Tom's costume wasn't that different from the Doctors - long coat, waistcoat, hat, just missing the scarf.
I would rate his performance in The Silver Chair as one of his best, and his Puddleglum is my favourite of his characters, after The Doctor of course.