Hi Susie,
I've just gone to Sipadan-Mabul-Kapalai. We stayed on a decommissioned oil rig in Mabul that is now used by Seaventures. Most of our dives were at Mabul. The Seaventures house reef has lots of stuff to see (scorpionfish, frog fish, flatheads, lionfish, beautiful nudibranches, anemone shrimps, etc, etc). Unfortunately the viz probably averaged around 3 to 5 metres. When we were there, the current on the surface was quite strong. The Lobster Wall was also interesting.
I was a bit disappointed when I first descended at Paradise in Mabul... there was just sand and poor viz (abt 5 to 10m) but after a while, we found the harlequin ghost pipefish, cleaner shrimp, hingebeak shrimps, huge turtles with remora, lionfish, flounders, squat lobster in feather stars, eels, etc etc. Oh yes, and folks go to Paradise during the evening for the mandarin fish (they mate around 5 - 6pm and this would be the time to catch them on film).
At Sipadan, we dived at South point, Barracuda point and a turtle cave. Saw lots of turtles and in particular at South point, there were white tips everywhere. Also saw large schools of jacks, some trevallies, sweetlips and barracudas. The turtle cave seems like a turtle cemetary. I guess it could be interesting but although the cave is not that small, I felt a little claustrophic in there. It was total darkness in there. Viz was about 20+m at these dive sites.
We only went to Jason rock and Cleaning Station at Kapalai. Both dive sites were nice. Viz was average here too. About 10 to 15m.
My dive comp logged 26 - 27degC for the water temperature.
Hope this helps.