In early November (2011) I went with 6 friends on a Sun Holiday Tours trip to the Costa del Sol (Best of Andalucia), and we were all very pleased with the company. Their price (ca. $1950) for a 10 night stay at an excellent hotel with all breakfasts and dinners included, and a very low single supplement, was an excellent bargain. So good, in fact, that we were nervous and looked them up on the web before booking.
Not to worry! Everything they promised was true, and we had an enjoyable time. Because it was off-season, we got upgraded from their usual hotel (Sol Aloha Puerto, which gets mixed reviews) to the Melia Costa del Sol. This was a new, clean hotel right on the beach, with every room (?) having an ocean view. The food at the hotel (buffets both for breakfast and dinner) had many choices and was always very good.
Our only problem was not with Sun, but with the tour company they use for the included tours. Everyone found VDT (Visit & Daily Tours) to be terrible: long and many pickup stops (often 16-18!); overly large tour groups (50 and more in a group!); at least one guide that didn't care if the group stayed together or got separated; tours in multiple languages; and more. Our fear is that VDT is Sun's only or -- Heaven forbid, best -- choice.
One other point: Sun is not open on weekends, which can be a problem if you need to reach them in an emergency. Nevertheless, we were very, very happy with the value we received and hope Sun does tours to other areas we'd like to visit.