Belize is an incredible country. Go. It will change your life and you may not want to come back--not as in extend your vacation--but as in "can I feasibly make a living here and survive."
First and foremost. The staff is incredible. By the end of my trip I actually felt like they were my friends. The regular bartender, Anthony is one of the best bartenders I have ever encountered. He is friendly and understanding. I actually thought he was the manager of the resort because I would see him up working at 6:30-7 AM while we were leaving the resort for the day and when we returned at 9:30 he was serving drinks. One thing Anthony understood more than the front desk staff was that everyone has their own needs. He understood we didn't go to Belize to feel like tourist. When Anthony spoke with us I felt like I was in Belize. Just another guy on vacation. Renne thought he was being welcoming and treating us like valued customers, but really he was condescending and made us feel like we were at summer camp.
Weather: Rainy season is fine. It will rain for 10-20 min then be sunny again. Also, it is kind of romantic when it rains at night.
Groupon: If your using a Groupon or not doing all inclusive, rent a car. Or rent a car anyway. Dinners at the resort are expensive and not very good. You can drive down the road and get way better food for 4$ than the 26$ they charge.(per person) Also having the ability to drive to the ruins yourself is great. We met a local guide who gave us a noticeably better tour than the what we heard from other tour guides at the sites. We paid him 10$ USD. We enjoyed him so much we hired him to take us across the boarder to Guatemala to visit Tikal. Go to Xunantunich and ask for Eddy at the ferry and they will find him. I will also leave a review with his number on the ruin page itself. If you go to Santa Elena or San Ignacio there is a restaurant called Corner De Colonel. It is the best and the staff is incredible. We stop here for directions and ended up staying for hours.
Local bar: If you want to get away from the resort La Cabana's is a local spot that is safe and tourist friendly. You will likely not blend in, but everyone is nice.