Greetings BFEIII, (and thank you for the comments drrich2 and Tater!)
St. Croix is rather unique in the surrounding islands in that we have a Pier (One of the Seven Jewels of the Caribbean), Canyons, Reef, Walls, Wrecks, and spectacular night dives all on the same island. St. Croix is great for beginners, advanced, tec divers, photographers, boat divers, and shore divers. Depending on what you are looking to see, you've several options to choose from.
St. Croix is ~37 miles long, 42,000 population, with winds/waves going from East to West. There are 5 dive shops, each with a particular focus, location, and how many people they take on the boats. The far east is sparsely inhabited and very dry with grasses, shrubs, and cactus. The middle of the island (Christiansted) is the heavy population center. The west is the Rainforest and large, green estates. No diving on the south shore due to the wave break. Almost nobody has a home or resort on this side due to the waves/winds (except Divi resort and Casino). It takes about 30 minutes to get from the far east/PointUdall/Divi to Christiansted and another 30 minutes from Christiansted to the west/Frederiksted.
+ The West side (Frederiksted-side) of the island the calm leeward/shadow of the island and ideal for calm diving. There are about 40+dive sites on the west, including The Pier and all the major Wreck dives. Long, gentle sloping terrain to ~55', then a drop off to about 100' is the overall profile on the West. Reef diving is unique in each location. Beaches are large and calm (Rainbow Beach, Frederiksted Beach) and great for paddleboarding. This western side is the home of N2theBlue Scuba Diving.
+ The NorthWest side of the island can have 2-5' waves and 100 yards off shore is the Wall dropping from ~40' to 900'+ deep and a rather steep slope. About a dozen+ dive sites total from SweetBottom to CaneBay.
+ The North-Central is the famous, underwater Salt River Canyon and served by several dive shops (N2theBlue, CaneBay, DiveExperience, and St. Croix Ultimate Bluewater Adventures).
+ The North-East diving is the barrier reef protecting Christiansted to a bit further east. Waves can be 2-5' most of the year.
+ The South doesn't have any dive operators and sparse diving due to the wind/waves typically come from this direction (ESE).
- Christmas Winds start around Christmas and last about 2 months. These winds can bring 5-8' waves along the north and south shores.
+ Whales can be heard late February and most of March. This is the time Humpback Whales are calving their young. 
+ Seahorses are everywhere on the Frederiksted Pier. Be sure to hire a Divemaster to point them out.
+ Turtles make a great sight all year. Green Turtles, Hawksbill, Leatherback... all grand.
+ Water Temp is ~77'F in February and ~85'F in October.
+ Water Viz ranges from ~120' on good days, ~60-70' on most days, and ~30' on bad days (higher winds/waves).
What are the MUST SEE DIVES of St. Croix?
(1) The Frederiksted Pier -- WEST/FREDERIKSTED -- One of the Seven Jewels of the Caribbean. Also, #1 place in the Caribbean to find seahorses. Its like diving a Gothic Catherdral with pylons reaching towards the sky and the stained glass windows are replaced with a dazzling display of corals and sponges. There are still two sections of the old pier (destroyed by hurricane Hugo in 1989) with over 50 years of growth, too. This dive site will easily take several dives to explore, from the end at 90' (known as Three Amigos), to the end of the cement walkway at 42', or near shore and the old Pier remnants at 20'.
(2) Night Dive -- WEST/FREDERIKSTED -- The Frederiksted Pier. Bio-luminescence is a highlight! Moreover, the colors EXPLODE at night under your dive-light! Also, there are other creatures that come out at night... especially Octopus.
(3) The Salt River Canyon / The Wall -- NORTH SHORE -- 100 yards off shore and at ~40' deep, the Wall drops to several thousand feet deep (deepest point: ~13,500'). This brings a diversity of life that is not often seen in the world. Because this is on the north shore, conditions can be a bit chopy/bumpy. Waves can be knee high or 5'. Salt River Canyon is a boat ride to get to unless you use one of the dive companies that have a boat directly in the Salt River Marina. Salt River is a prehistoric underwater carved canyon/river/waterfall. Brilliant.
(4) The Wrecks -- WEST/FREDERIKSTED -- A: Deep Wrecks (2 @ 72-110'); B: Shallow Wrecks(3 @ 35-60'), C: Armageddon (the massive wreckage of the old Pier dropped at 90-120'). These are all quite close to each other.
(5) The Reefs -- WEST/FREDERIKSTED -- Calm waters, extended dives, and water features that can have the dive be 30-55', or 55-120'. There's a ridge on the west where dives can be either deep or shallow. The waters are almost always calm because this is on the wind-protected side of the island. The cover-story of a magazine was divesite: The Swirling Reef of Death. You'll have to ask for the funny story from the captain. There are over 40 divesites for both shallow and deep dives that'll keep you delighted. Very easy to book a 3-5 day package and see a lot! HUGE beaches for the non-divers, stand up paddleboarding, and the charming laid-back rest you've been looking for.
Please note: When Cruise Ships are in port, the US Dept of Homeland Security does not permit diving on The Pier (until after it departs).
Loads of options for dive companies that will rent gear, guide dives at the shore, or take you on a boat dive.
TripAdvisor.com is a great resource to find out more. Lots of parking 100 steps away from The Pier.
As for food and restaurants -- ahhh, well. There are so many to talk about! Again, TripAdvisor is a good start. A few favorites come to mind: Pier69, Polly's Cafe, Lost Dog Pizza, Rose's Dream Cuisine, Rowdy Joes, Eat, Angry Nates, Savant, Pickled Greek -- and SO MANY MORE for that one particular dish or night of the week when they feature what they're known for (Coconut's sunday texas BBQ, Turtles after Dark's drunken lobster, etc.).
Enjoy your travels and Enjoy St. Croix!
