To be honest, I don't think it's a very good EP. They put so much effort into making the pets customizable, but then you get them in-game and there's really not all that much to be done with them. Still, since it's the only way to get actual pets in the game and I really wanted a sim dog, I haven't had many regrets from buying it.
Some people say they're too needy, the dogs in particular. But Annaliese has the right idea; they're as needy as the traits you give them. With the right combination of traits my sim's dog hardly ever bothers him for anything. The world is nice compared to the ones which have been released after it. It does rain a lot there. You can walk your dogs in the rain, your sim will just get wet. There are a lot of sick strays, but to me it's not a world-ending issue.