For me, at least, it's being unable to load it in a background tab or copy the actual URL from the URL bar. It breaks the web.
Plus who needs to lose even more screen space to that stupid bar at the top plus the fact that the browser chrome doesn't hide itself when you scroll like it does on a normal page?
I haven't had a super awesome experience so far with it on my iPhone. I've seen a lot of results where I click on them and they spin forever, never loading. But if I long press and open the result in a new tab, it loads instantly and works fine.
Yep, in the short-term it's a good thing for users because it means they can access the content they are looking for more quickly in a consistent format.
In the long run, it might be bad for users, as it could result in media producing less valuable content, and one big company having more control over distribution.
Since I've searched for the content, these are not ads but real content that match my search query which site owners have asked Google to render. If, despite matching my search query, the content is not what I'm looking for, then it helps me as a user to know that sooner rather than later.
(That being said, I dislike it as a content provider and as someone worried Google has too much power)