The concrete issue is flight search. When you google "flight from a to b", rather then seeing search results linking to websites for flight search, the first thing you see is the results of Google's own flight search. Is that wrong? What about image search? When you search for "skyline berlin", you'll see images of berlin's skyline, before you see links to other image search sites.
Same is true for a lot other stuff. If you search "timer", you'll see a timer, not links to various timers that look ugly as shit.
As a consumer, I love it. So much easier.
On the other hand, google could take over almost any business like this. At least, any business that is "functional" in the sense that the only thing you really want is to get some output based on your input.
There's a clear tradeoff here between what's good for consumers, and concerns about democracy, the concentration of power, etc.. And also innovation. Why start a new company, if google can just take over everything?
There are only two clear, non-arbitrary rules: Search engines are only allowed to show a list of links, or search engines can show whatever they want.