Has anyone stayed at the Riu Ferrara Hotel in Torrox in December? What was it like?

Did they have any entertainment on in the evening?

I have not been to the RIU Ferrara in Torrox, but I do know the area, and since no one has answered your question, at least I can give you a basic idea.
The RIU chain of hotels has an excellent reputation. Most of the large chains of hotels have evening entertainment several times a week. either shows or live music. RIU is no exception. In december it is considered low season until Christmas week, so the amount of entertainment up to then might not be overly expansive (It would depend how full the hotel is).
Torrox is on the eastern coast of the province of Malaga near Nerja. There are plenty of things to do in the area, especially if the weather is good...You might even be able to take a swim in the Mediterranean if you don't mind the water being chilly. (The hotel has an inside pool for the winter also) You can visit the Grottoes in Nerja, go to a shopping center in Velez-Malaga, or even drive to M谩laga itself and visit the Picasso museum (for example). (It's less than a half hours drive).
If you head in the other direction after Nerja you have the town of Almu帽ecar, also nice for a day trip, lots of nice restaurants and a lovely beach (In Granada the "tapas" are served free with your beverages almost everywhere, great for filling your tummy without much expense).
Good luck with the weather, this area has the best winter climate in all of Europe, but we do have some rain once in a while!
Have a nice stay!