We love St. Croix as a vacation destination and have bought land there with hopes to live there one day soon. I guess it depends on what you like and what you are looking for. Due to the size of the island there is certainly something to suit most tastes. As mentioned by Nutmeg it is further away from the rest of the USVI and BVI and travel there is not as easy as to St. Thomas. That said you can fly there from the mainland connecting through Miami, San Juan, Atlanta, Boston and probably a few other cities depending on where you live and what carrier you prefer to fly.
As for vacation there are many options from hotels, resorts and rental homes/villas to suit most budgets from very high end to what I consider reasonable. There is a VERY good selection of places to eat again from casual to upscale, Nice beaches, hiking, snorketling and other water sports as well as some interesting historical sites. There is some cruise ship traffic during the season, but it is very minimal compared to St. Thomas. Interesting shops and crafts made on the island as well as the Crucian Rum Factory. I guess one of the negatives is the closure of the oil refinery which has greatly affected employment specifically and the economy in general. Recovery of the economy is delayed there but that has also led to there being some good real estate deals! Really depends on what you like. If you can be more specific, I can try and be more helpful. There is not usually much chat about St. Croix on this board.