Marsan is an actor who can be sympathetic and reprehensible at the same time; and then because his Norrell has never been either a total write-off or obviously waiting to be redeemed, he generates an incredible amount of audience goodwill once he finally starts behaving like a person.

Yes, I think this is exactly right. I think Marsan captured Norrell very completely and very generously.

I'm not sure I saw him as fully when I read the book. His covetousness and secretive selfishness, combined with his desire for prestige, put me off. But what you say about his having taught himself magic *without* the natural flair that Strange had--that immediately warms me, and I think you're absolutely right that his way of approaching magic is precisely the road for magic to return on--so completely alien to the Faerie sensibilities. And yes: very, very human. That too makes him a good foil for Faerie.