Northanger Abbey is supposed to be a parody of the Gothic Romances that were popular in Jane Austen's day, and I can say that A Sicilian Romance does lend itself to parody.
I picked up my copy of Ann Radcliffe's second novel a few years ago at a second hand book shop, mostly because Ann Radcliffe's books are discussed so often in Northanger Abbey. I will say that I found the book amusing and frequently hysterical in its plot contrivances that required a full suspension of disbelief and was left wondering if that might be the reason why Henry Tilney likes them.
I would recommend reading them if you want some light reading and enjoy melodramatic journeys
A Basic Summary: No this doesn't include everything that happens, but it does include spoilers regarding how everything is wrapped up in the end.
The story itself is told by a traveller to Sicily who is entranced by the ruin of a castle that once belonged to "the noble house of Mazzini" be makes friends with a friar and is permitted to read the manuscript containing the castle's history, from which he wrote the story itself. The story itself is set in the late 1500s and its main character is Julia, who along with her elder sister Emilia, is the daughter of the fifth marquis of Mazzini, a haughty, stern and, cruel man and his first wife a charming a beautiful woman who died suddenly. Following her death, the marquis remarried and headed off for the city of Naples along with his son Ferdinand and his new wife, a beautiful but vain, proud and deceitful. The daughters were left in the care of a relative of their mother's whose life story could have been expanded into its very own horrid novel (as Jane Austen called them).
The two girls are raised never leaving the grounds of their father's estate and never having any outside company except for infrequent visits by their father, but they grow to be incredibly beautiful, and talented, and intelligent, and graceful, and kind, and sensible, and etc. The long passages describing their many perfections were one of the things that set me giggling. Then their father returns following the death of a trusted servant and decides to put on a huge house party at the castle. Julia falls in love with the young count her stepmother wants to have an affair with. The stepmother is already upset because Emilia and Julia are so much prettier than she is, and are such beautiful dancers, and so popular and etc. and is not made happier when her would-be boy-toy takes a liking to Julia.
The count and Julia attempt to elope, the count dies in the process, Julia is locked up and informed she will marry a duke and then escapes. Much excitement ensues before the good end happily and the bad unhappily. You will need to read it for yourself in order to find out exactly what exiting events occur and how precisely they resolve themselves.
The image in this post is of the cover of the Oxford Univerisity Press's 1993 World Classics edition of the novel.