This was written around the same time as the Lord of the Rings trilogy, and people compare them as though they have to choose which one will ascend to some fantastical throne. The fact is, they're about the same high quality, but with different tones. Gormenghast is dark and gothic in all the right ways. I compare it more readily to Edgar Allen Poe. And for all the years I liked Poe, when I read Gormenghast I felt I had encountered something Poe had been reaching for. I really enjoyed this trilogy, as a whole. The second book is probably the best and could stand on its own, unless you want more of the characters, the mood, the primal humor. And just fyi, the last book was interesting in academic ways and disappointing in essential ways.
One last thing: Gormenghast is meant to be read slowly. It's funny I should say this because I never do it, but it's like those fancy wrappers that insist that to truly appreciate dark chocolate, you must allow it to melt on your tongue- not chew it. Such could be said of Gormenghast.