From my experience, some things are just better done indoors (eating, playing concerts). Outside you have to worry about wind if there's more than a little of it, uneven or soft ground than will make tables tip over, bugs pestering everyone, allergies for some people, etc. And of course, power might be troublesome.
It does sound pretty novel otherwise, and a lot of people will probably show up just for the fun of it. Some might be turned off by the inherent problems, but I suppose there's a chance you'll get a dedicated group who would do it again.