We did Sabah about 12 years ago as a family holiday with our 2 boys who were about 15 and 11. I think it was about October we went. I think of all our holidays we've had, it is one best that comes to mind. My memories are of seeing my boys laughing and smiling by all the experiences.
KK is just another asian city, and it was a bit saddening to see how much deforrestation for palm oil was happening even back then, but the (12 day?) tour was fantastic.
We left from KK and did Mount Kinabalu, Sungai Kinabatangan, Pulau Libaran, Sepilok Orangutang sanctuary, Mulu National Park, Kundasang War Memorial and a couple of other islands and places I cant remeber.
We were very lucky with our tour(cant remember who it was with). It was basically the 4 of us and 2 guides (one was a trainee). They were from rural areas and knew the places really well. They would do things like tell us were to stand at the Orangutang sanctuary, as they know where the animals would go to (directly in front of us) and at the turtle sanctuary they knew the rangers, so the boys got a side tour and got to handle the hatchlings and even got to release some of them. We toured a few islands out that way.
Kinabatangan River was great. We stayed on the river and did different day trips. The monkeys had the kids in laughter all day, we got lucky and saw Orangutangs in the wild, but the miniature elephants are very elusive.
Mount Kinabalu was great too, in fact the worst part of it was KK, but we arent really fans of visiting cities.
On the way home we stayed over at Brunei. Very different and surprisingly we enjoyed it. We stayed at the Empire Hotel & Country Club. It wasnt overly expensive, and its service and facilities was over the top. Even the capital, Bandar Seri Begawan, was very lay back and enjoyable. Just remember its a dry country (but you were allowed to take in some alcohol for consumption in your room).
Jerudong Amusement Park was ok too. The dodgem cars are full on smash up derbies, and for a massive amusement park, there wasnt many people there.