I definitely wouldn't classify them as the most difficult, but they're up there in the lists.
IMO many of the really frustrated posts are from people new to keeping snakes or who haven't really done their research on any of the Candoia in particular. They are definitely not like most of the other boas & pythons out there and not a snake I'd recommend for someone who isn't already experienced with snake keeping. Proper husbandry is an absolute must with these guys....anything less causes major problems. However, the sucesses with them far outweigh any difficulties in my book.
Parasites can be an issue, especially with wc animals. Most of the wc you can purchase will already have been treated, but it doesn't hurt to keep an eye out for problems. I never tried frozen herps for food with my one picky eater, just live frogs, geckos & anoles...none of which worked for him BTW...although I do have a friend on anther forum who uses f/t geckos for one of her Halmaheras. I ended up having to force feed my guy after a few months because he started losing weight (he was probably a couple of years old when I got him, about 12 inches and wc). What eventually ended up working for him were pinkies/fuzzies bred from wild caught field mice that my Mom raised for me. He snatched those right up from the get-go. It's really all trial and error with these guys to find out what works best for your particular animal. Once you get them to feeding for a few meals, then you can worry about switching them to rodent prey if they don't already take it.
Do avoid frequent prayer to the diety of your choice, I'd recommend purchasing either an older animal, or one from a reputable breeder who already has them feeding on pinkies (such as Jerry Conway or Central Florida Reptile Breeders). Older animals tend to take rodents more easily than babies and aren't quite so fragile as neonates can be. With proper care...and plenty of patience, lots & lots of patience sometimes...the babies can be real rewarding. As was mentioned to a poster below, don't expect quick growth, or for them to like temperatures in the range of most other boas, and don't overfeed - these are some of the most common mistakes with people new to these little guys. Once you get the basic husbandry requirements right and allow them to settle in, things tend to go smoother. I guess the main thing is to know that these little guys aren't going to bend to our expectations, we have to adjust to them...and they're more than worth it IMO. 
Raven