Hmm, it's been a long time since I've seen a movie in theaters, let alone a hidden gem or grossly misadvertised one. I try to avoid ads like the plague.

The only recentish thing that comes to mind is Barbarian, but I don't think I even saw an ad for it. Not one I paid attention to. Just went randomly, it was not as expected, and we had fun not taking it too seriously anyways, which seems appropriate for that movie.

Others elsewhere in the convo are making some banger recommends, though.