My daughter went on a PGL holiday (horse riding) last year and absolutely loved it.
I would have no hesitation in recommending them. The accommodation was functional and practical but not luxurious, but the organisation, the activities, the care of the children and the catering were of an exceptionally high standard.
It was my daughter's first time away from home, though she had been itching to go away for a while having two older brothers who have their "own" holidays each year.
We had no problems with homesickness, they seemed very good at managing any issues, she made some lovely friends and was sad when it ended. In fact she asked if we could book a second week for her straight away she loved it so much.
Our work circumstances mean that summer holidays are rare as a family so it's nice for the children to have a break of their own during the six week school holiday.
Personally I think it's great for their independence and confidence.
The only other children's holidays I have experience of are Scripture Union which are equally good and run a wide selection of different experiences - some very sporty others more arts and crafts based. However they obviously have a heavy Christian ethos so don't suit everyone. We are a Christian family so they are to our personal taste.
This year my daughter is off on her second PGL to do multi-activities this time which covers a wide range of sports and outdoor fun. She is already counting the weeks down !!
PGL is not a cheap holiday though you can expect to pay upwards of £500 plus extras if you buy their insurances and souvenir kit bags.