I work in the Caribbean a lot, and of all the islands I go to St Lucia is my favourite, although it does require a little bit more effort to winkle the fun out!
The island is not big but as others have noted the roads are very windy and mountainous. Local drivers do tend to just go everywhere with their foot flat to the floor no matter what they are driving, so first tip is to get a car/taxi everywhere rather than bus. A bus will make you sick (this is one of the biggest sticking points from my work colleagues when we go here!)
Next, be aware that the island is split into 2 main holiday areas - the packed touristy north around Rodney Bay, and the quieter west coast. The south and east coast are very windswept, with no real beaches or accommodation at all on the east and only Coconut Bay on the south. Along the west though is beautiful. This is where my favourite bits of the island are.
The hotels along the west coast tend to be more exclusive, but there are cheaper places to stay if you look. I have stayed at Fond Doux and Marigot Bay. I can highly recommend both of them. They are not your typical Caribbean beach holiday though.
Fond Doux is a working chocolate plantation, and the accommodation is in old colonial style workers’ bungalows. My children loved it there, and the owner was great fun. There was a shuttle bus to Malgretout Beach (at the foot of the Pitons) every day, there were lots of chocolate-related activities (we did a family ‘learn about chocolate’ day which culminated in the kids making their own chocolate bars,) you can walk out onto the Tete Paul jungle trail, and within easy reach are the Pitons (worth a climb if you are in St Lucia,) the sulphur springs at the volcano, the botanical gardens, Souffriere, and you can get boat trips from here. We were here for 5 days but be could have easily spent 2 weeks.
Marigot Bay has an all inclusive hotel resort and lots of self catering accommodation. It is a hurricane hole - a narrow inlet sheltered from the sea and surrounded by the village and lush jungle. It has been used for various film sets, most recently Pirates of the Caribbean. It’s quiet and peaceful, but a little further away from Souffriere and after boat trips and relaxing in hotel there is little to do. A pretty place for a few days though.
I also have stayed in Rodney Bay. This is not a great location unless you are keen on bars, water parks, and other stuff you can get in any generic holiday resort in the world. It backs onto a large town, and this is where much of the ‘unsafe’ feelings come from. After we’d had the 5 blissful days at the Pitons, we came up here for 2 days of beach and my kids couldn’t wait to get out of there. Says it all, really. Even the sand on the beach is imported, because the sort of holiday maker who books this type of place is put off by the fact that St Lucia is a volcanic island and the beaches are naturally rocky and dark grey, so they brought in acres of yellow sand from somewhere else (it looks a bit like yellow builders sand to me, and it destroys the natural marine environment where they have put it.)
There are a couple of places further north that get a decent reputation - the Body Hotel and Windjammer, but if you want real luxury Caribbean here I would head back down along the west coast and go to either Anse Chastenet, or (if you have won the lottery!) Sugar Beach. I think Anse Chastenet would be better though, it has an eco philosophy about it and engagement with the local community that I like.
For all those saying 2 weeks in St Lucia is too long - I think you have perhaps not ventured very far around the island or have stayed in the wrong part of it. I could stay there much longer! It has some truly world class snorkelling and diving along the west coast, and amazing boat trip opportunities, as well as the absolutely gorgeous jungle interior - evenings spent under a growling thundery sky as the frogs bleep and the fireflies flash is an unforgettable experience. You mustn’t forget it is in the tropics, and is a rain forest island. Those complaining about the weather - rain forest needs rain to be rain forest!
I have a work trip there next month, just one night, and writing this has made me sad I don’t get another night there.