I visited Ko Ngai solo in April 2012. Because I thought it would appeal to Lady Tezza who likes small islands and better than budget accommadation, I took her there in our December 2012 trip. Much was unchanged in the short period between trips: you can read my island report here https://www.travelfish.org/location/thailand/southern_thailand/trang/ko_ngai
The following I thought worth adding to my previous info:
* Paradise Resort still not operating. This is the backpacker/flashpacker joint on its own little beach in the south-west of Ngai. It was shut down in April, I thought maybe an early close after high season. But it was still not operating in the second week of December. Hey this is well into the Andaman high season and getting close to peak - some dudes were doing a bit of work on the place but their English was not good enough to tell me if they were trying to get it ready for the rush. Any feed-back would be appreciated.
* The boardwalk between the main eastern beach which contains most of Ngai's accommodation and Ko Ngai Resort on its own little beach in the south-east of the island was cactus - looked like wet season had been real tough and junked it.
* For some of the best views in the Andaman, make your way to Kohgnai Cliff Beach Resort's (at the far northern end of the main eastern beach) pool - this is at the highest point of the resort (and any place on this beach) and has a gob-smacking outilook on the nearby karst islanda, mid-distant Ko Muk and Ko Libong and the rugged mainland coast. This is the resort I took THE BRIDE to and despite the low tide blues (no problems, just walk up the rather gorgeous beach to deeper water at such times), it proved a winner.
Here's the good news - the mama-san running the resort told me outsiders are welcome if they spend a bit on food/drinks at the scenic poolside cafe. Okay - large Changs are 30 baht more than budget Ko Ngai Villa up the beach, but the views are worth way more than that - but the 95 baht chicken sandwich with fries is considerably cheaper and waaaay better. Anyway we told some budget travellers who came down from Ko Lanta with us on a daytrip longtail and they spent some time up there. Budget resorts and some of the adjacent mid-rangers like Coco Hut and Thapwarin don't have pools, so if you are staying in these joints, get yourself up to Cliff Resort's pool.