We (me, dd1 aged 9, dd2 aged 7, dniece aged 6, dnephew aged 10, dsis and dsis boyf ) went there in May 1/2 term. The children all said they enjoyed it, but I thought it was really quite dull. It's been there for years, and closed a few years ago, reopening when Dr Who came back on the TV. There is only 1 room relating to the new series, the rest is, as Babyblue2 says, old and dusty.
The woman on the reception desk couldn't get her head round our request for 1 family ticket, 1 adult and 2 children, so charged us a random £22.50 (where it should have been £37.00). I am glad she had issues with maths, I would not have been happy if we'd spent £37 on it.
Having said all that, the kids did enjoy it.
We went to the one in Cardiff earlier this year, and IMO, that one was better (although smaller). It was free as well, when we went, although they seem to be charging £4.00 now - not sure if they've made it bigger.