There is a reason why some books continue to be important long after they were written. Frankenstein is as much a treatise on the meaning of life and the very concept of humanity as it is a work of horror. Sure, it's not as terrifying now as it was when it was first written. Of course you've seen The Munsters since this book was written, so your concept of the square-headed clumsy monster (that isn't the way he's portrayed in the book, by the way. He speaks fluent French and is quite agile)has probably dulled you to what readers in Shelley's day found to be absolutely terrifying.
This book is as important as it is great, and it surely is both. It is the first notable work of science fiction ever written, and remains one of the true masterpieces in the genre. It also shook the dust off Gothic fiction and gave the genre legs enough to keep moving into a new century. Finally, it is now and will remain a major cultural touchstone. Your very life will be enriched by reading this book.
If you give Frankenstein half a chance and accept it for what it is, rather than what you think it should be, you'll enjoy it.