You need hype to get someone to pick up a new book these days. There's just so damn much to choose from. What's going to get someone to pick up Book A rather than Book B? Well, lots of people raving about book A will generally help.
And to get a lot of people raving about Book A you do need Book A to be pretty damn good. Nobody is going to rave about a book that was so-so or just decent.
But there's a second edge to the sword that cuts through all that noise, and that second edge can cut you instead. If a book gets too brilliant a press, if the readers are too hyped up, too excited ... then they expect to open the book and sit there twitching and slack-mouthed as each line sears itself unforgettably into the back of their skull, filling them with the kind of literary ecstasy that can only ever be remembered from your first great fantasy book and never recaptured no matter how many times you revisit that same story.
And if your new novel does not leave the hyped reader in a spent and satisfied pool of their own juices. If it turns out merely to be a great read, merely a 5* novel ... then there is always the risk of backlash, always the risk of it being rated and reviewed against what they had imagined it might be from the hype rather than against the competition.
So, hype, a necessity and an evil.
What about the third edge? Oh, I just tossed that in to hype it up. Who wants to read about a boring old two-edged sword?