Be aware that it's a new timeshare property, mirroring the Westin Ka'anapali and Ka'anapali North. So you'll get a timeshare pitch.
That said - these properties are much, much better than the Westin (or Sheraton) just down the road. And there's a shuttle between them, so you can still get to Black Rock to snorkel.
I've done 5 nights at Wailea/4 nights at Ka'anapali North, and stayed in Ka'anapali multiple times. Our family much prefers the Ka'anapali area. Nothing wrong with the Wailea, but we just find more to do between Lahaina and the north tip of the island. And getting upcountry - Makawao, Haleakala, etc - isn't even very different, as you still need to get to mid-island from Wailea.
In terms of quality/unknown - I have no doubt that Nanea will be a great property. We were at Ka'anapali North, next door, a month after it opened, and it was great.