The hype came about because the Church condemned it for casting doubt on the divinity of Jesus. A lot of people sat up and thought, "what's this book that's got the Church all in a twist?" and went out and read it. Thus it quickly became a global bestseller...a qualification which is easily confused with being a really good-quality read.
I agree that it's nothing more than an entertaining yarn...but a lot of people out there read too much into it and made it much more than it ever should have been.