Hi Aquamusette,
I just got back from a 6 day Undersea Explorer trip last week! We had an amazing time - I wholeheartedly recommend UE, particularly if you are interested in marine research. We didnt choose the best time of year to go but we still had a fantastic trip. The crew were awesome, the food was great and the trip is excellent value for money. We spent three full days on Osprey reef - something the other boats dont often offer - and UE has only once been unable to make the crossing to Osprey: a few years back when there was a cyclone. She's a very stable and comfortable ship, even if she has a few miles on her - I like to think of it as "character"! Dont expect five star accommodation but do expect clean, perfectly comfortable and roomy cabins, a recently refurbished saloon and lounge and huge top deck with plenty of shaded lounge space.
Being very enviro-concious they are also the only boat that do not do a shark feed - instead they run a shark attract which is (they say) equally effective and more ecologically sound.
Im planning on writing a trip report as soon as I have a spare hour or so. Feel free to PM me or post if you have specific questions.
BlueSun