It's been 4 years since I've been in the islands, but I found it one of the greatest experiences of my life.
That being said, I found this to be so perhaps because I've been exposed to many different cultures and backgrounds, having lived in NYC for 27 years, and consider myself somewhat adventurous.
It's definitely a third world country, and if you've ever been to the Caribbean you may find Grenada and St. Vincent's to be a little less 'civilized' than some of the tourist-dependent countries there. Much of the landscape is more of a raw beauty than the finely groomed type you'll find in other islands also. But I feel this adds to the adventure and the experience in general.
I lived in l'anse aux epines, a sort of upscale area of the island not far from school. It was an old villa with a studio apartment, cable tv and internet, new through the wall, remote control air conditioning and washer/dryer on premises. It had a pool and a view of the ocean, with an acre of fresh fruit trees such as banana, grapefruit, mango, and orange. It cost $550 US/month including everything. I'm sure that is much more expensive now, but it was quite luxurious. I usually took the bus to school because it stopped about 200 yards from my house, but took me to my door after dark. I usually used the bus to get to the grocery store also, a very nice, modern store with most US brands of just about everything you wanted, and nice fresh vegetables.
The people of Grenada can be grating on your nerves if you've never been exposed to a culture like theirs. They are definitely on 'island time' and don't make much of a fuss over being of great service when you're at a restaurant or at the store. Unfortunately, many of my younger, non-worldly colleagues mistook this as rudeness, being unable to empathize with the people whose country we were guests in and treated the locals with contempt. I never had a single confrontation with anyone while I was there and spent many days at the beach or up in the rainforests, both of which are beyond description in their beauty.
Go, and enjoy the uniqueness of the experience.