Is Gormenghast worth reading?
Oh yes! 
It is, more than anything, a tale about the castle Gormenghast, from which the trilogy (usually found bound in one doorstop of a single volume edition nowadays) gets the title. This is an immense place filled with history, danger, junk and dust. And weird people. There is the Groan family, the nobles, who are weird enough, but in addition there are a myriad other people who keep the whole place running. It is almost undefinable as to which category of fiction it could be placed in, though it does tend to be seen as fantasy. But it also has strong elements of gothic horror and satire.
The main narrative thread follows the adventures and machinations of Steerpike, a kitchen boy who has escaped, and now seeks to climb the social ladder of Gormenghast, along the way upsetting the established order - which in itself is stifling and inexplicable. Some of the best characters include: the sinister Flay - former manservant to Lord Groan, Fuchsia - eccentric and romantic daughter of Lord Groan, and the Prunesquallors - the castle doctor and his man-mad sister.
I'd recommend reading it before seeing the BBC version - as then your imagination will be able to run riot imagining the gothic splendour of the place.
