The Metaverse, I guess? It's funny how living in a virtual world has been this hyped-up concept for decades and it finally comes out and it's just kind of...lame for lack of a better word. Maybe it's too early to tell, but it feels like the Web 3.0 Metaverse push hasn't lived up to the hype.
Aside from that, I'd say the Xbox Kinect. Maybe it's just me, but I remember that when the Kinect came out there was a lot of hype about how it was going to revolutionize how people played games. But I don't think we ever really got a Kinect game that lived up to that hype. To be fair, I remember a lot of articles of people doing interesting things with Kinect it's just that none of them really had anything to do with gaming.