I've been to Blackpool zoo several times a year for the last 3 years now and have always had a great day.
Although it's not the biggest zoo you will ever visit, it does have most of the impressive animals, such as lions, tigers, giraffes, gorillas and sealions, along with lots of other smaller animals like otters, kangaroos and monkeys.
The zoo is really nicely laid out in lovely grounds, so it's got a nice spacious feel to it and in the Summer there are plenty of places to spread out a blanket and have a picnic.
The cafeteria has quite a lot of tables inside and several outside. Only on the busiest days (school Summer holidays for example) have we ever struggled to get a table. The food in the cafe is pricey, as you would expect in a place like this, but the hot food has always been really nice. Even my extremely fussy kids have always cleared their plates!
There is a great penguin enclosure (new in 2009) and feeding time is well worth watching just to see the penguins battle it out with the seagulls for their dinner.
There's a childrens area of the zoo with lots of farmyard type animals and also a small petting zoo area which is great for young children.
Although I'm not an expert, to my eye all the animals looked happy and well cared for and the enclosures looked clean and well maintained.
You can easily spend a whole day there and you feel like you have seen everything - in some ways an advantage over the other bigger zoos where it's a struggle to get round the whole place in one day.
If you are a Tesco shopper, it's worth noting that you can use your clubcard vouchers to buy admission tickets (you have to do this in advance by ordering them online).
For any family with young children this is a great day out.