I went there today.
I was picking up my Merlin Annual Pass, taking advantage of my newfound moneys and the MAP sale, and I just thought to myself 'why the hell not?'. It was a bit weird being by myself in there, as it was mostly young families. But I enjoyed it. The exhibits are all very well done, with lots of interesting animals. The crocodile in there was actually moving, and seemed rather happy - I've never seen a crocodile move before, even in a zoo, so to see it swimming around was really nice.
Sadly, the penguins were closed today (no idea where they went), so ill be sure to return when they are back. The piranhas were also missing.
Overall, I'd say it's pretty good. I wasn't paying attention to how much it costs as I only cared about my MAP, but I'm sure with the usual 2-for-1 vouchers it's not too expensive.
Being honest, I was also in there to see if there was any hidden SW7 advertising, but I didn't see any.