The Sims 2 on the PSP was a bit of a flop. I think that this was mainly due to the atrocious loading times. The game was constantly loading and this meant that gameplay was never smooth. Unfortunately, The Sims 2 -Pets doesn't really solve this problem. Whilst the general gameplay may be improved it is still hampered by constant loading. You may be halfway through placing an object in your home, or in the process of training your pet not to pee on the floor when the game freezes for anything between a split second and five seconds. This, at first, is only slightly annoying, but as the game progresses and you have more and more to keep track of it becomes incredibly frustrating.
Admittedly this is a big game and there is a lot of content but surely it doesn't need to load as much or as often as it does. Plenty of other games manage to do perfectly well by loading everything in one go, so why can't this game. GTA:Vice City Stories, whilst having some pop up issues, manages to run smoothly even though there is a huge city to load. Daxter runs smoothly even with the massive levels that need loading there. And neither of them are constantly loading.
The Sims 2 -Pets would be a great game, even a fantastic game, if it wasn't dogged by this problem. I feel it is a waste of time describing the merits of the game because they are completely overshadowed by this one, huge problem.
Avoid at all costs.