Serenity -- sort of been sliding for a couple of years. Probably wouldn't recommend at this time.
Hamanasi -- beautiful place, but it's not in Placencia. It's in Hopkins, an hour north by car.
Nautical Inn -- comfortable rooms in octagonal units imported from North Carolina, nice pool.
Green Parrot -- most of the units are Mennonite prefab cottages, two level, with a couple of newer cabanas. Pleasant beach.
Maya Breeze -- variety of units including apartments, cabins, rooms. None is "primitive" and indeed really no place on the Peninsula but a few basic places in Placencia village would be considered primitive.
All of these places I've stayed at and like (Serenity's current situation excepted). Hamanasi is a big step up from the others, but again it's in Hopkins.
The Placencia peninsula is quite different from Ambergris Caye, and I think the main decision is which place you would prefer. The peninsula is 16 miles long and some of these places such as Maya Breeze and Green Parrot are away from things. There are not nearly as many restaurants, clubs or shops in Placencia, and of course parts of the peninsula, mainly Placencia and Seine Bight villages, are still struggling to recover from Iris. Also, off season even in a regular year Placencia is MUCH slower than Ambergris Caye, and later in the summer a few hotels and restaurants close completely.
Belize books and publications by Lan Sluder:
Belize First Magazine (http://www.belizefirst.com
Fodor's Belize & Guatemala Guide (new 4th edition coming this summer)
Adapter Kit: Belize (the first and only comprehensive guide to living, retiring, working and investing in Belize -- a best-seller on Amazon.com)
San Pedro Cool (the first and only visitor guide to Ambergris Caye)
Belize First Guide to Mainland Belize
UpClose Central America
Belize Book of Lists