There are three primary luaus on Maui. There is one at the Hyatt, one at the Marriott, and Old Lahaina Luau. The Old Lahaina luau is the most authentic as far as luaus go. After spending lots of time in Mexico, we decided that authentic luaus are probably like authentic Mexican food...not as romantic as it sounds. We opted for the Hyatt.
You are seated with 300 of your closest friends, and if you get there early enough you can sit near the stage. This is a good thing. There are long tables with a waiter assigned to each table. She/He brings you free drinks (alcoholic or not). The food is served as a buffet and is very good. The ambience is better after the sun goes down.
The show is the star of the evening. It's a high energy show featuring scenes from various Polynesian cultures. It's very interesting. Is it authentic? Who knows! But it's fun. The entire production lasts no longer than three hours at the most which is just about right.
Also, they uncovered the roasted pig, climbed a palm tree, split a coconut, taught a hula dance to volunteers, and just generally had a good time. The show was written up in the Hawaiian Airlines magazine.
If you've never been to a luau, forget about 20 friends sitting around a circle eating. Go to one of the luaus in Maui and have a good time. It's just fun.