3D movies, I remember everyone being so excited for shit like Avatar because it was a 3D movie without the dumb red and blue lenses. Then it turned out to just give you vertigo.
Or even 4K TV. Like it looks marginally better if your face is jammed into the screen, but all it really does is suck up way more bandwidth and cost $400 more.
I was so fucking excited for Evolve, because it was supposed to be made by the people who made L4D. And then it was, uh, what it was.