We stayed at the Marriott Waikaloa in November, but we used Bonvoy points and stayed on the hotel side. It's a combination hotel-and-timeshare property with the hotel rooms in different buildings than the timeshare rooms. Everyone shares the common area facilities I think. It's a nice, though somewhat dated, property, and our room was ok but had a leak in the bathroom resulting in water that came out from under the flooring when you stepped in the right place. I reported it and hopefully they found and fixed the problem before it became a bigger issue.
I can't speak to the timeshare rooms. But the resort has a nice pool complex, a good restaurant with a great breakfast, a bar, etc. It's well located in what I'd call the tourist hotel area of the island where nearly all the high-end hotels are clustered. There are multiple golf courses, two shopping centers with dining options within easy walking distance, it's right on the beach, and you could probably have a good time without venturing out, but you should venture out.
The island is huge and you could spend a week just driving around to see it all. If one of the two active volcanoes is erupting, you'll want to drive to see that if you can. When we were there, both were erupting and you could see the glow from Mauna Loa from the hotel area. We also spent a couple of nights at the Volcano Hotel on the opposite side of the island, inside Volcanoes National Park, which allowed us to see Kilauea's lava at night.
If you've never been to the Big Island I definitely recommend it. All the islands have a different look and personality, but the Big Island is the "most different" in my opinion. Because of past lava flows over the years, nearly all of the undeveloped parts of the island look like some kind of alien landscape. It's stark but beautiful.