Had a 3 generation trip here over the Easter weekend and everyone thoroughly enjoyed it. Highly recommend it, especially for primary aged kids, it's the sort of place you could keep revisiting as children get older too.
Dd (4) loved being able to pull levers, turn knobs etc and the adults got a lot from it too.
We spent over 4 hours there, and took a picnic (plenty of space) so although it was £5.80 for adults we all felt it was good value.
I suspect it might be a place to avoid during term time though as I'd imagine it will be popular with schools.