Pets is a great addition to Sims, but there have been better Expansion packs.
Well, the obvious thing you can get with this Expansion is, well, Pets. From Hyper-active Chihuahuas to Hypo-active Tabbies. In my humble opinion, while these pets can give you a life-long buddy, they also take up space, and money. You can buy them a multitude of luxuries, from doggy-mansions to cat towers. Granted, some of the luxuries are required, and some can be quite funny. IF you get a cat, you'll need a scratch pole, but you'll love the catnip mice. The dogs will require a chew-bone, and if it's an indoor doggy you'll want, get a doggy-bed, as well.
Along with at-home pets, you can also find strays. You can easily adopt pets, too, just call a pet adoption agency on your phone. And that's not including the skunks. Don't anger them or prepare for a sudden drop in hygiene. You also can find wolves around your neighborhood. Any of these pets can get onto your lot if you don't have a fence. And if you they do get on they can start digging up that dirt that holds your lot together. You can always just chase off a pet, but they'll be back again, and again, unless you spend a couple 100 or so simoleons on fencing up taht empty lot of yours.
Don't get me wrong, I love pets, they just take a lot of money and space, and then you've got the wolves. Watch out for yellow-glowing eyes in wolves, and if you see one, don't get too close, and don't get to friendly, or prepare for a Werewolf! Werewolves go from human to their true form at night. When as a werewolf you can attack another person, causing them to become uglier werewolves. Werewolves have all of the same needs as humans, they just look different at night