Looks like you will be there just in time for typhoon season!
I spent 5 years there and loved it. If you like white sandy beaches and 84 degree turquoise water filled with tropical fish and coral, you will love it. It is pretty warm and humid, but being in the south, you are pretty use to that.
SCUBA diving is outstanding, as is fishing, snorkeling and hiking (known as boonie stomping there). There are nice restaurants, a mini-waikiki like tourist area and Guams famous Fiestas, basically big parties hosted by various villages on weekends. You might also want to visit the islands of Saipan and Rota just to the north of Guam.
Definately drop me a PM if want some specific recommendations!