Today we visited http://www.sheprethwildlifepark.co.uk/Html/SWP-Home.html which is great because we can go on the train from Cambridge and it is about a 2 minute walk from the train station. You also get money off entry prices with a valid train ticket!
The girls had a great time. The place isn't huge but most sees include the big cats, wolves, otters (my girls' favourite), a cool walk though bat cave with them flying around you, a bit where you can stroke bunnies and a large indoor and outdoor play area. You could easily spend most of a day here, especially if you take a picnic.
I suppose some of the cages are a little small and some of the animals pace up and down looking a little stressed but I don't think it is any worse (and probably better) than a lot of other small zoos.