I've been to quite a few of them, and the intensive programs and I thought they were great.
Like turtleface said, they hire amazing teachers, who make it interesting and although it is mostly revision, it's still worth it. I'd recommend the intensive workshops, although they aren’t cheap, they are really good for sciences and maths as you get a lot of practise and help. The lectures for English and history, I thought were great as they tell you about some great outside texts to use for English (who would have thought to do a bob the builder episode?!?!) and then history lectures are great as well!
If you have the time and money, I would defiantly recommend them!