Don't ever underestimate Moloka'i for quiet and slow pace. If you need activities, don't go. You won't like it. But Molokai certainly has it's aspects.
As others mentioned, it's great for quiet and relaxation. For activities on the island, there's the trip to Kala'aupapa. Then there's taking the drive to the end of the island, and, perhaps doing the hike to the waterfall. After that there isn't much to do except go to the beach and take it easy.
Except for Ni'ihau Moloka'i has the highest proportion of native Hawai'ian ancestry. IMHO, that affects much of the character of the island. The people of Moloka'i by nature are less accommodating of things that they think will disrupt their traditions and values. They gladly and willingly accept that the consequence is less commercial activity and more poverty. When we were there I perceived an attitude that if those things are important to you, perhaps you should relocate to another island.
On the other hand, if you want to get a glimpse of what Hawai'i used to be like then Moloka'i is probably where you want to go.
For ourselves, we found the people gracious and friendly. But then, no matter where we are we don't engage with local residents as tourists. I know almost everyone says that, but the reality is that a lot of people who act like typical truly believe they are not acting that way. And I'm sure that includes us more often than I would probably like to admit.
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We plan to go back at some point It's not our top place to visit, but it certainly fits into our rotation of places to visit when we are in the islands.
DW has a co-worker who spends at least one week on Moloka'i every summer. It's very restorative for her.