They're slowly strangling it now with obnoxious ads. These days I typically get an awful video ad before the actual video, a pop-up ad that obscures the video during the video, and I've even started to see cases where they interrupt the video in the middle for another awful video ad. I get that they have to make money somehow, but I think they're going to start strangling the goose that lays the golden eggs if they don't back off some.
It's not yet bad enough to say that they killed YouTube, but I'm afraid they might get there.
Most ads I see are skippable these days, and the uploader can't set an overlay ad and a video ad on their videos. Vevo videos has those annoying "check out this other artist" thing on the side, but I assume they have some special deal in their contract, because no one else seems to be able to do that.
It's not yet bad enough to say that they killed YouTube, but I'm afraid they might get there.