We stayed at Rimba in May. It was great. 6 of us for a birthday weekend away. Rimba organises your personal pick-up from Singapore (if there are enough of you - otherwise you meet at Newton) and then drives you straight across the border, through Johor and to the pier - where the boat is waiting to take you to Sibu. Far too easy!
The resort is great, rooms / huts are simple but that's what we wanted. We did a dive on Saturday, at a nearby island. It was great. A few of us took advantage of the massage / spa on site as well - idyllic. The rest of the weekend was spent in the sun. :)
The crew - particularly on the bar - are lovely and very chatty - they want to make your stay as good as it can be. The food (three meals a day are included in the price) is fantastic and there's a fair amount of variety.
Only other consideration was that neither the room price nor the drinks were super cheap like many other places in Malaysia - but for the food, the crew, and the general atmosphere of the amazing beach, I think it's good value.
Definitely recommend it.