I stayed there in May and enjoyed it. I would stay there again, and have stayed at other moderates, deluxe, and economy on property, but I haven't yet stayed at Caribbean Beach and it may have a slight advantage as I've heard. As others have mentioned, it is very large and spread out and you will do quite a bit of walking. It is indeed a beautiful property, offers nice views if you have a water view room, and you can see structures around the property from upper level rooms in the Casitas such as the Tower of Terror, Swan and Dolphin, Blizzard Beach Summit Plummit, Tree of Life, etc. depending on your room location. It is VERY quiet, relaxed, and is quick and convenient to all parks except the Magic Kingdom. Getting to Downtown Disney was a bit a of problem early in the day as the busses are few and far between at that time, and if you have tight time constraints for dinner reservations, a cab may be the way to go for D.D. though very pricey.
It offers a health club as well which is more elaborate than the simple "fitness rooms" at most hotels, and has some limited spa type services (massage, etc). I made use of the business center while there, using the internet connection and shipped home some purchases that wouldn't fit in my luggage easily. It was handy to have! Busses were never an issue but dont linger if you see one coming when walking to a stop, as they tend to bypass any stop if there isn't anyone standing there waiting.
The hours of the main building's shops/restaraunts during my visit were extremely annoying. There were no posted hours for the food court, Mayan Grill, the gift shop or arcade and each didn't seem to close at the same time each night during my 5 night visit. One night (a Tuesday) the small food store attached to the food court where you can pick up items for the in room fridge, snacks and such was open past midnight, the next night, it was closed by 10:30pm, the next 11:30pm, etc, and my final night, wasn't open at all when I got in from the parks around 9:45pm.
I would suggest Casistas or Cabanas if you dont want to walk as far and definitely do an online search for or ask your travel agent or Disney to provide a property map and request specific buildings/room locations when you book your trip (no guarantees though!), and definitely politely and VERY nicely work with the cast member when you check in to see what rooms are available. I have always had luck with choosing my room location (in my price category) if checking in early enough in the day, and cast members have always been informative, helpful, and accomodating. Though with Magical Express, I'm not sure if this would cause a problem with your luggage being misdirected if you were originally set for a different room location by the booking system.