Think of everything you've ever heard of about Dr. Frankenstein's monster - that moaning, groaning, imbecilic abomination. Now throw all of that out the window, because the original novel is so startlingly different (and surprisingly good!) that it may as well be completely unrelated.
In my opinion, it's worth the read because it's such a classic novel. It is indeed a good story and not all bad, but it feels extremely simple, borderline naive at times. But then again, you should always consider it was written by a 19 year old in 1818. Times were different. As I said, is not all bad. The message is great: As Kathriller said "man's power to create and (in the process) destroy".
A beautifully written novel offering so much more than the film adaptations. The depiction and later narration of the monster CREATED by Frankenstein is wonderful and puts a whole new perspective on your surroundings and fortune.
I try my hardest to avoid referring to the creation as a monster. Shelley knew how to tell the best kind of horror story: the kind that demonstrated man's power to create and (in the process) destroy. Will always be a favorite.