There are a number of questions along the lines of "What should I do/see in [place]?". Are these on-topic?
A generic question like “What should I see in [place] in X days” is not a good Stack Exchange question. The proper answer to this is a guidebook for [place]. Such questions should be closed (as “off-topic” or “not constructive”). Example: What are some of the sights to see in Budapest, Hungary?
Another kind of question that doesn't work well on Stack Exchange is one that requires answerers to cater to the tastes of the asker. Subjective questions must meet quality criteria that are mentioned in the “don't ask” section of the FAQ. Questions that boil down to “what's your favorite sight in [place]” are not a good fit; reserve them for chat. Example: Something to do in or around Colmar in France
More focused questions asking for possibilities do have a place on this site. The specificity can be a particular interest that is not addressed by most guidebooks. Example: In the Loire Valley, are there any "arty" caves that can be visited? It can be a constraint that is hard to meet without expert advice. Example: What to show grandparents in Stockholm/Anytown? The idea is that a good question will invite answers that inspire thoughts like “that's interesting” or “wow, I didn't know this”, not “I like/don't like this”.
One of the trends on some other sites is to realize that closing is not permanent. Closing is something to be done while a question undergoes major editing, partly to motivate the asker but mostly to prevent irrelevant answers.
So, someone asks "what are great things to see in Paris?". It gets all kinds of comments like "how long are you going for?" and "what time of year?" and so on. It also gets closed, quickly. The OP answers the comments, and either the OP or some caring people with edit privs fixes the question into something that will attract good answers. They add a few constraints, enough that it's not an ordinary guidebook request, but not so many that it's too localized. They add details and get people interested enough to write good answers. Once that's done, the question can be re-opened, and it didn't attract any useless answers during the edit period.
When you look at it this way, you close early and close hard - but you communicate with the OP, and don't just turn your back on the question. That way the quality stays high and the OP gets their question answered.
There seem to be a spate of very open/broad questions in the past few days. So it's probably best to make a decision quickly and early then stick to it.
- Are they just too open with no "one right answer" as per the Stack Exchange rules? If so start suggesting how to ask more specific questions and close them.
- Are they good questions for Community Wiki? If so state this and convert them to such.
I guess it's up to the community, the pro-tems, and the SE people how far to "bend" this specific rule and/or how much to use Community Wikis.
Note that on the big SE sites there have been lots of discussion about whether Community Wikis are a good thing at all. Please feel free to add links to any of them here...
If I were enforcing the SE rules as they are currently written I think I would have to close them, but perhaps this is the time to make an official interpretation of the SE rules.
(And that's not even thinking about how subjective these questions are...)