I've had two experiences with 'Ohana. The first was quite a while ago, when I was around 8 or 9 years old, and I remember it fondly. I can't remember what we ate, all I remember was that the service was really great and the activities were a blast. My father hated it, because he can't stand any dinner where he is "bothered" (so he'd hate 50's Prime Time Diner as well, haha), but I liked how everyone was extremely friendly and called us cousin.
It was a very inviting experience.
Went during the week of November 15-21st (sorry, I know you were asking about Thanksgiving week), and it was an experience I would rather forget. My husband and I are both vegetarian (I slip some cheese into my diet on occasion, though I'm primarily vegan), so we ate differently than others but in no way was this the negative part of the experience. The food wasn't bad at all, in fact 'Ohana probably has the best tofu you can find on Walt Disney property, but the service was a bit sad.
No one called us cousin, the air conditioning was on extremely high and even with sweatshirts on we were freezing. We had several people come to our table repeatedly with meat and shrimp skewers. One server approached our table timidly and literally tossed our salad down on the table and left without a word. Another man came to our table with a huge skewer of shrimp, and though he was friendly, he was instant.
"Would anyone here like some shrimp?" My husband looked up at him for a moment, looked back down at his tofu dish and smiled and said, "Oh, no thank you. We're fine here." The man with the shrimp kept staring at us and asked again, "Are you two sure?" We just nodded and smiled and he walked away after a few more awkward silent moments.
A couple other servers came to our table with skewers of pork, looked at our dishes, blurted out "OH" loudly and then walked away. This wouldn't be so bad, except we never actually saw our own waitress until 45 minutes later. We sat there with empty drinks for most of the evening. She was nice, but that was about it. She was just nice. We had much better service at other restaurants. This was the only restaurant we actually wouldn't visit again.
While I think the restaurant has definitely declined in terms of service, I don't know if it declined food-wise. If the service thing wouldn't bother you, and you are big meat-eaters then this still might be a viable spot for you to dine. I also know my expectations were much higher than they should have been going in.