Hi

,
We have also visited Center Parcs on numerous occasions and have had some very enjoyable short breaks.
Personally, our favourite 'site' is Longleat Forest. They have a new Aqua Sana Spa center there, and there are a variety of treatments on offer which DW tried out. I only visited there for the 'try out' session were you pay about £20 for three hours trying out all of the different 'rooms' like the ice room, herbal room, japanese zen room, relaxation room etc.
The natural beauty of Longleat is also our favourite (although we have never visited the Oasis one in the Lake District). The covered plaza at Longleat is also ideal when the weather turns inclement.
We stayed in a 4 bedroom villa with some friends. For about £20, when you book you can choose the exact villa you want (subject to availability) as we like to be close to the centre and lake this was ideal, as otherwise you may be miles away, and with a 4 year old son this comes very reccomended to you with a 3 year old son!
We took our own bikes, but they do rent them at the parc. Bikes are an essential IMO.
We also liked Sherwood, but for us the travelling distance is a bit far and it seems a bit 'dated' compared with Longleat. We didn't enjoy our stay at Elveden - the facilities were poorly maintained and the chalets were not as well equipped as in the other resorts.
We loved the restaurants at the resort too. Hucklebury's is a brilliant American themed restaurant with a great indoor play area with children. We also enjoyed meals at the pizza place (Lucianos??) - Their buffet is a must. Plus, you have to try The Pancake House - delicious!
The swimming pool 'The Subtropical Swimming Paradise' is amazing and you could spend a whole day in there. It is always heated and there is an outside section with a brilliantly fun river rapids attraction.
There are so many activities on offer like Tennis, Badminton, Squash, Cycling, Football, Basketball, etc. All of them are at an extra cost (the only thing free is the swimming pool). They also book up extremely early at peak times so book before you arrive.
If you have any questions, please ask.
HTH
Richard.
