We've been to Belize many times, and we love it. We've been to Maui, Bonaire, Aruba, Caymans, Turks, Puerto Rico, and many US Beach destinations (San Diego, Miami, NC/VA) etc and loved it...but we knew exactly what we were getting, every time, and our expectations were adjusted accordingly to what each country had to offer.
If you are looking for the type of service offered by a US 5 star resort, similar to that of Kea Lani Hotel in Maui, then there is no need for you to visit Belize - go to Maui. This country is located in Central America folks, and that alone needs to be taken into consideration. Nothing is guaranteed - not electricity, phones, TV, AC - those are luxuries in a 3rd world country, not essentials!!!! Many Belizeans live without them today.
And if you still want to visit Belize, by all means, do no stay in Belize City....there are so many more beautiful, undeveloped areas to see (Caye Caulker, PG, Placencia). Its one of the best diving sites in the world, boasting the 2nd largest barrier reef. The fishing is absolutely amazing....and the food's not bad either, but you have to put it into it's correct frame of reference. The service will not be like that of a US Hotel, and it's a "go slow" attitude, so trying to rush will only make it worse.
If you want adventure and something off the beaten path, wear shorts & t-shirts, no shoes, and have the ability to laugh at yourself, then by all means go and check out Belize. It's quite endearing & charming with so much to offer...but it is not Maui.
When looking for accomodations, make sure you ask if they have AC, TV, phones etc....that's the only way you will know, because not every room, at every hotel/cabana offers these luxuries, and they will cost you extra.
Set your trip up on the right foot by asking the detailed questions. Don't "expect" that these things are naturally included, because they are not.
If you want 5 Star Service on the ocean, I recommend booking your vacation at the Kea Lani Hotel on Maui. It will cost you 5x's more than visiting Belize, but at least you will be happy.