After becoming fascinated by her masterwork Frankenstein, I wanted to dig deeper into Mary Shelley's bibliography. So far I've read, besides the aforementioned Frankenstein, Valperga, Falkner, Perkin Warbeck and Lodore. And, being honest, I find them all to be great novels. I still consider Frankenstein to be her best work but I wouldn't say it's her only masterpiece.
I may consider Mary Shelley to be one of my favourite writers of all time since I truly love how she's able to craft stories with overall good pacing and, at the same time, being able to have deep, thought-provoking characters and themes. The fact that she's known mainly for Frankenstein (Which, yes, is in my top 5 favourite books ever) makes her, in my humble opinion, one of the most underrated writers of all time.