Having spent 3 weeks in Sabah over the Dec/Jan period and staying at SL Rasa Ria for part of that time I found it not so unexciting. There is plenty to do. Horse Riding, water sport activities and plenty of other things to do. The one criticism I would have was the lack of food variation at the restaurants in the resort. You can pop into town for that but this can be a schlep and the shuttle bus only runs 3 times a day from RR to TA resorts. The taxi ride can become expensive if doing it regularly. We stayed at the Hyatt for one night only as a transfer for our flight to Brunei. I personally would not stay at the Hyatt for more than a night or two.
Sandakan certainly is a strange mix. The east is truly different to the west of the island. Off the top of my head cannot remember the great restaurant on top of the hill. Travel warnings are just that. Warnings. We felt safe the whole time we were there.
I went to the Australian War Memorial in Sandakan which is quite moving and informative.
Maybe Brunei for a 2 or 3 night stay would allow you to see something different in Asia and the opulence of the mosques.
The Empire Hotel and Country Club is a nice getaway for a few days.
If you have any other queries give me a buzz.
Highly recommend Sabah as a destination. ^