We visited Warwick Castle for the weekend (and stayed at the Knight's Village, review submitted separately!) and had a great day.
First off, I need to say that on the Saturday, the rain stayed away and so we were able to enjoy most of it. Day 2 was spoilt a bit by rain but the kids still managed to enjoy what they could.
We have kids who were 4 and 5.5 at the time of the visit and they were kept distracted/entertained enough throughout the day, so that says something for the appeal of the place!
Having enjoyed a walk around the outside of the castle, interacting with the resident peacocks etc, we ventured into the inner section, across the small bridge and under the portcullises and the ramparts. I've read that people don't like the fact that there are food vendors dotted around the site - personally I didn't find them too intrusive (i.e. they weren't brightly coloured and they weren't surrounded by litter etc). You have to expect these kinds of things at these popular attractions.
We enjoyed walking along the ramparts for a section, but had to turn back once we got to the huge tower (which you can't by-pass), as having to climb all those stairs was beyond our kids.
The Princess Tower is a nice touch, engages the kids for 15-20 minutes and is nicely done. The 'Princess' tells a brief story and lets the kids interact with her and never lets it get to drawn out or boring.
We only got to see the Bowman show briefly from the ramparts but it looked good!
We did, however, get to see the bird show, 'The Falconer's Quest' 3 times and it was well worth it. The show is fantastic, even in drizzle (which we had on the 2nd day) and both of my kids loved it. They have a good selection of birds (from memory - Stellar's Sea Eagle, Harris Hawks, Bone Eating Vulture, Bald Eagle, Peregrin Falcon, Hawk-Owl and one enormous great bird the name of which I forget but it was as big as me and I'm 6ft 1in). Most of the birds are allowed to fly above and over the audience, some of them (the smaller ones) deliberately fly very low (in fact we routinely had to duck, which the kids loved) and you get to see them in flight up close. It's all very well done and there's also a story aspect to it, which also makes it more engaging, not that it needs to be.
The bird show really is a highlight of the visit and I recommend that you do it more than once - the best position is right in the middle of the seating area, so you get the birds flying right over your head.
Overall, considering it's 'just a castle', we really enjoyed our visit. They really have tried to make the whole place better than your average castle site and as a result they've made it interesting, engaging and there are some fun aspects for the kids too, which is a real plus for those with young kids.
We'd happily go back for a day out, I imagine it's even better in better weather.