what's something you watched because the poster made it look awesome and it turned out really lame?
For me it was Roots Search (1986)
I don't know if it quite counts... But I'd say basically every single NES game, and most other early games. Man... Incredible box art back then... But damn if that box art had anything whatsoever to do with the actual game.
Downsizing. One of the most misleading advertising campaigns ever. One of the worst movies I've ever seen!
Men in Black 1.
Maybe not exactly the poster, but the preview. It was awesome, quick and funny.
But then the movie was long, slow and not very funny aside the jokes that were already in the preview. But we had seen those often enough already. Disappointed