Sports- or activity-based meetups tend to be the best of the bunch, as do expat gatherings when you have just relocated to a new country.
I have been a part of a few meetups, and I think that Meetup the application is great when you have an existing community that you want to bring online. If an email list isn't enough (and sometimes it isn't) meetup can be a great way of extending an existing community online. However, if all you're doing is meeting once a month, Meetup is overkill.
It may work OK for generating new community and connections, but as the parent said, you need to have some staying power, and that is either going to be related to some kind of revenue (leads, etc) or some really dedicated hosts that will probably burn out in a few years.
Pretty spot on. As an organizer, you're worried about turnout and interest along with the logistics. My thing is now, just let others do the organizing and show up and leave early if I want to.
That leaves the people who have something to gain - "new in town" groups run by real estate agents, tech meetup groups run by recruiters, etc etc. These communities tend not to develop a long-term following because most people can smell the opportunism from a mile away.
The best Meetups tended to be run by professionals - non-profits, museums, etc, who have something to gain but tended to be aligned with the interests of the participants. Those are sadly few and fr between.
I liked Meetup for a lot of uses, but you really did have to sift through a lot of cruft. I think their problem isn't really any execution failure, and reflects simply the level of difficulty of community-building.