I [...] In Shadowmarch, though, unlike MS&T, the menace is ratcheted up until you almost feel you're reading a ghost story. Williams knows how to build an uncomfortable atmosphere until you're scared - but not quite sure what of - now THAT's brilliance.
Williams' talent isn't so much about inventing new things to go into high fantasy, it's in the quality of his writing - he's writing high fantasy in a different manner. He can really write, and I can see how he's improved (which doesn't make me a whit less enamoured of his earlier works). If Williams wrote in any other genre he'd win the Booker prize, or something equally prestigious, for Shadowmarch.
But don't let that put you off if you hate contemporary literature! Williams' writing isn't contrived or showy, just quietly brilliant. He's always focused on telling the story and, I'm sorry, I disagree that he switches viewpoints too often - I think my fellow reviewer just is snatching too-small pieces of time for reading, and though I sympathise, you really have to give an author a chance. You wouldn't intermittently listen to your mp3 player at the theatre, would you? That's why Williams 'caught' him later than other readers would be caught - because he WILL catch you.
I think this would be a good book to read as your first ever fantasy novel, which is the highest praise I can think of. Other than that, just read it, people! (NB the first book in Memory, Sorrow and Thorn is 'The Dragonbone Chair' - and don't forget Tad Williams' stand-alone book 'The War of the Flowers', or his more sci-fi-y 'Otherland' series - all are more than worth your time).