The worst thing they did this with was Island Sanctuary.

During one of the Fanfests, they showed a concept art of it. Then it went into radio silence for over a year, perhaps even a year and a half.
Then finally we got an update during a LL, but it was just to show the size of the island.

During this time, people's expectations ran wild, fueled by some reports that an interview with a dev had said it would be closer to housing, and Animal Crossing was also fresh in peoples' mind.

And then we got IS.