I won't go into detail about the stories themselves except to say that I think that the 1st 2 books of the trilogy are in my top 3 fictional books in modern English.
The 2011 hardback Vintage Illustrated Gormenghast Trilogy is an improvement over Vintage's previous edition (which was Meridian's beforehand) in that they've got rid of some of the flagrant typos that were such a blight. Unfortunately, a lot still remain. They seem to be the result of bad optical character recognition (and inadequate proof-reading), e.g. "torn cat" instead of "tom cat", "day" instead of "clay", "splinteririg" instead of "splintering"! That doesn't explain "corosive", though. Don't these people have a spelling checker? I'm sure the edition I gave to a friend in 2001 didn't have nearly as many typos; alas, I can't remember the publisher.
Those who've seen previous editions will be familiar with many of Peake's illustrations. This edition has more of the same (though, for some reason, the picture of the starving girl, whom Titus takes home to Juno, has gone).