Depends on what the group is like.

The traditional adult halloween party involves costumes and lots of alcohol. Went to a LOT of those in my 20's, a few in my 30's and now you couldn't PAY me to go to one. LOL

The parents' halloween party involves adults, generally in costume, taking all their kids trick or treating, having some kid games maybe, and just hanging out, eating, answering the door and chatting while the kids play. Went to a LOT of these in my 30's.

If you really want to do something different and worthwhile, you could have a "Treats, No Tricks" party. We had several of these for various charities I volunteered with over the years. You pick a charity to support, ours was usually the local humane society. You go around to local businesses and ask for small donations ... pens, keychains, gift certificates, etc. Then you get a group together at your house, have some food and chit chat first, then you go door to door in costume. You tell people you are collecting treats for Charity-of-Your-Choice, and have a labeled coffee can for donations. Then you give them a treat ... one of the small prizes from the businesses. It's a lot of fun, people love it, and you can get a lot of money for a good cause. Its a good idea to advertise this in your local paper first, so people know it's legitimate.