I never did the Luau, but ate at Ohana last year in September. The food was good and plentiful, but the service was slower than mud and the place is very loud. Of course, the scenery is very beautiful! There are large windows that you can see a great view of the castle from, I think pretty much any seat would be okay to see the fireworks, but you'd need to be right up at the windows for the best view.
The service was friendly but slow. We are not big eaters, so that didn't bother us not getting as many meat "refills" (for lack of a better term) but we like our soda and water and that was very, very slow to get to us. The servers seem absent alot of the times...I mean, I didn't see them serving other guests, so where the heck were they? A carafe of cold water on the table would fix this problem.
The dessert was good, the bread pudding with bananas foster sauce and ice cream, but I know there are disers that prefer the old dessert of pinneapple and caramel.
The atmosphere is very nice, with the live music and the games for the kids. It is festive and touristy. The food I'd say is no better or worse than those chain Brazillian places, the Sabor Di Brasil's, etc...just grilled meat and lots of it. The shrimp was amazing, but that is not on the menu now (maybe the 25 shrimp my DH ate cleared out the ocean???) The sides are tasty.
If you don't mind slow service and a loud but neat atmosphere, it is a good place to visit at least once.