The place is absolutely stunning! We spent 5 days there and still feel like we didn't have time to see enough.
Caves are fantastic - many are available as show caves and quite easy to explore (though you may need to climb quite a few steps up and down). But adventure caving is something else. We only had time to do the easiest - half-day trip to Racer Cave, but even it requires you to be quite fit (some rock-climbing experience would also be helpful).
No tripods alloved in the caves - you will need a special arrangement with the park. The most convenient place to stay is at park headquaters (see my separate review).
Surprizingly, there isn't much wildlife in the surrounding jungles to be seen as the canopy is too thick and the jungle is the real deal. We could hear a lot of birds, but barely spotted any even after spending almost 2 days in the Tree Top Tower which we booked for private use. Probably it was a wrong season too. A longer trip to Camp 5 and Pinnacles would probably be more successfull in terms of wildlife spotting, if you can handle such a long hike.
However, if you are into insects - that's the place to be as there're lots of them. There are many reptiles too once you know how to spot them. Which brings me to the next topic..
The guides that work at the park HQ are not very experienced. As I've been told (but cannot verify) a lot of older guides quit due to disagreement with the management, and the new ones are not even officially licensed. We could tell by the absence or totally erroneous information they were provided during the guided walks, and one female guide doing night walks could only spot a few insects at her eye level without bothering to look up and down. Generally, I wouldn't recommend night walk to anyone even though it's not at all expensive - going in a huge crowd along the tiny path with a so-and-so guide you won't see anything but rather scare it off. Go on your own instead at some other time - there's plenty of marked paths around the park to choose from.
Our guide at adventure caving tour was fantastic, though I think he was a freelancer doing work for the park. I would probably search for a guide like this if I ever go back to Mulu again - it makes all the difference!
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.