Maxis is still trying to draw in new users and with this game, it just might.
You now can look after pets! Real ones too, not just some fish or guinea pig (if you have Livin' Large). However, the excitement of having a pet quickly diminishes as you are faced with having to look after it.
When you adopt a cat or dog, you may choose their gender and breed. In real life you'd choose them because they are friendly and gentle, on the Sims that just doesn't happen. Instead, bars are awarded at random – if you're unlucky, you'll get something with hardly any points. If you are, well, good on you. I kept quiting to the neighborhood and reloading until I got a pet with at LEAST average points.
After you get a pet, there's a rush of having to look after them. Loud pets wake you up when you nap, while quiet ones tend to slink away. Grouchy pets snap and guests and deny contact, while friendly ones will always want more and get steadily upset as you can't provide it. Lazy and playful, slow and smart, independent and loyal. I found the ideal pet was high in all stats but friendly – then the were perfect without demanding attention, and more likely to successfully drive away a raccoon or skunk (find out for yourself) although the later still... well, kicked up a stink.
Unfortunately, even if you don't adopt a pet, your yard will be littered with strays who think your lawn is a public restroom. As soon as you move in, get a Hydrant for dogs (Decorations, Other) and a Litter box (Other, Pets) so they won't mess your lawn. Alternatively, you can download the free (and, in-game, much cheaper) Stray Away pet deter. Works wonders. However, if you use the former method, then you can go out to pat the strays if you're lonely (it's often good to include a full Pet PlaCater too).
Although it may sound like I'm listing all the BAD things of Sims Unleashed, I'm really just drawing your attention to things you need to consider – in reality, this game is great. New objects, interactions, and a center for shopping! You can even plant your own garden to put in a pantry and, if you don't have the skills for a job, have a farm and earn you living that way by going to Old Town back to sell the grown vegetables! Note though, you can't collect seeds from your produce, you have to buy more.
All in all, this is a great addition, if only it didn't lose that New Feel so quickly.
A last recommendation, www.thesimsresource.com provides excellent skins for your new pets and old Sims. Even Sims 2 stuff if you're looking to buy.