Thought I'd reply to this as I have been to Grenada off and on the last 12 years. Been there about 8 times. Got married there (then later divorced back in the U.S. haha), became an instructor there, and have sent quite a bit of stuff down to donate to an orphanage as well as several computers to a school, and my trips are almost always several weeks+. My answers to your questions are below.
Questions:
How does the diving compare to other places we have been in the passed? (Roaton, Cozumel, Grand Cayman and Nassau):
-Depends what you prefer to dive. There are a lot of really amazing wrecks. Don't miss the opportunity to check out the Bianca C. I dive it every time I'm there. I also really like the Veronica due to the abundance of life around it. The underwater sculpture park is neat too. There is plenty of diving to be had and many of the wrecks aren't too far.
Is there any good shore dives?
-Like Wookie, I've never seen anyone shore dive in Grenada and I've been all over the island.
Which dive shop would you use?
-Devotion 2 Ocean and Aquanauts are both great operations. D2O is connected to The Rex (actually I think it's formally called The Grenadian operated by Rex Resorts). I wouldn't stay at that particular hotel as it is a bit high end and a little far from Grand Anse and St. George's but the dive shop is excellent and all of the staff is incredible. I did my IDC there. Aquanauts has a shop at True Blue. I have spent time at True Blue with family that was staying there (I was staying at a different location). They love it. You can get deep discounts there at SkyAuction. Seems to me they've never paid more than around $70/night there. Both dive shops are great and I don't recommend one over the other. Dive with both and get a feel for them. Hopefully the Course Director of D2O will be around for you to meet. Her name is Ruth Collymore. She's a lot of fun to be around!
Do you think it is safe for hiking and shopping on our own?
-Yes. There are quite a bit of vendors and they can, at times, try your patience. I've never seen one get violent. St. George's is always pretty busy with lots going on. Many nights there will be guys with BBQ carts out selling chicken. You'll be safe walking around at night in those locations. I've walked down more off-the-beaten-path places at night. Use common sense. I wouldn't suggest it with your wife and daughters and I'm usually armed when I do it (but the machete's primary purpose is as a tool, not for defense). It isn't a Grenada thing, it's an everywhere in the world thing.
How is the food?
-I do a LOT of spearfishing when I'm in Grenada so it's super fresh and delicious. The nice part about Grenada is they have local culture (unlike Roatan, for example). I adore an item called the "roti". They come in vegetarian, chicken, and lambi (conch) most commonly. It's got vegetables, lots of curry, and is put together in a dough that is cooked. It's hard to describe and I'm not a chef. I just know these are DELICIOUS. Fish is always fresh. Nothing beats having fresh fish with fresh fruits and tea for breakfast. I exclusively eat sea life when I am there.
Any other information you think is important to know about Grenada?
Lots. But in terms of the major things:
-U.S. Dollars are easy to get around with. You'll get your change in EC so you won't have to worry about converting.
-I always rent a car when I am there, if you decide not to, there are plenty of taxis alllll over the place. Public transportation is suitable as well, but whatever you do, do not board a bus when you aren't at a bus stop. I know two people who did that, 75 feet from a bus stop, and the police pulled the bus over and made them get off. Don't ask me why, I've never understood that one...
-If money is no object to you, try eating at The Aquarium. It'll set you back a ways, but MAN it's good stuff. They also sell cuban cigars if that's your thing.
-When visiting the Carenage in St. Georges, make a point of eating at The Nutmeg. Economical, delicious, great place for a roti if you don't want to find a hole in the wall a few streets over.
-I like to recommend staying at The Gem Holiday Beach Resort. Usually it's around $80ish a night. I like it because it's a full apartment, great views if you get a room in the front which includes a balcony. I love having a kitchen. I've never had problems doing a BBQ on the beach too. I like the bar as well. It isn't everyone's cup of tea though. Yes, there is a club on the property that I've been in but is pretty much exclusively frequented by locals. Friday nights it stays lit up pretty late. Some people get upset by that sort of thing. If you are one of them, then you might not want to stay there. True Blue is nice but they will also have events at the restaurant downstairs. I would NOT recommend the Flamboyant (bland considering its name), or Grenada Grand Beach (too Holiday Inn-ish for me and really expensive). Hotels range from around $70/night to several hundred a night. There's something for everyone.
-When you go into town, wear pants. You will stick out like a sore thumb and look foolish wearing swim trunks around town (I've seen it). Locals in Grenada know how to dress nicely. While you won't be hassled for wearing shorts (in most places...I wouldn't try walking into a bank like that...), you will definitely be targeted much more by vendors
-Getting trinkets and taxis around where the cruise ships come in will cost significantly more than elsewhere (common sense)
-MUST SEE ATTRACTIONS: Annandale Falls (take swimwear, you'll likely want to get in), the nutmeg factory in Grenville, Grand Etang Lake (don't suggest touching the mona monkey but he likes candy), pick up some awesome nutmeg soap from Arawak Islands off Maurice Bishop Hwy, Clarke's Court Rum Factory.
-I do a lot of shopping at Spiceland Mall for groceries. Dairy products are expensive so be prepared. Most other things are high too but dairy is highest. Buying local brands of stuff helps. Rum is priced really well. Clarke's Court is some of the best rum on the planet.
-When you leave the airport, don't be scared by how your driver gets around. Everyone drives like that in Grenada. I'd be MORE concerned if they WEREN'T driving like their hair was on fire.
-If you buy from vendors, which I have done quite a bit, haggle with them. They all have the same necklaces and stuff and if one doesn't want to play ball, someone else will.
-"Bug of the night", that "GLEEEET...GLEEEET...GLEEET" sound you will hear hundreds of during the night is actually a small frog...