If you're around to see this OP, I can review for you based on last year, and I promise I'm not their PR!
We went the last 2 years, really enjoyed it, but won't be going again this year as twice was enough.
Actually, the first year we really enjoyed it. The highlight was the Father Christmas, who was brilliant, the best one ever. However, last year it was ridiculously packed (whether we got lucky in '08 or unlucky in '09 I'm not sure) and didn't feel exclusive and worth the magabucks it cost us. The Santa was not nearly as good, kept getting DC's names wrong 
08' the DC were 6, 4 and 2, and I was pg. The four year old DS especially loved it, that is the perfect age. 6 year old DD twigged that you weren't really going to lapland via a magic tunnel, but managed to suspend disbelief and enjoyed it. 2 year old smiled through it and we got lots of nice piccies. A bit frustrating that a 2 year old is full price, as she was too little to ice skate, didn't eat any of their food, etc.. etc..
In '09 at 7, 5 and 3 they all enjoyed it again, and the 3 year old was able to join in with everything. New baby was 6 months or so, so fairly cheap.
This year, although the DC have been asking, we're not going to do it again. The older two are too old to get masses from it, the baby too young, and its so expensive for a family our size.