Some people were disappointed with Partners in Time...I can see why, it's quite a bit shorter and it eliminates the Zelda-like overworld in favour of a simple hub world. I like the hub world a lot better, and the story was a little more "epic", but it is definitely on the short side and lacking in side-quests or mini-games. It was also a little easier, I think. In spite of that, I actually like it better than the first.
Overall, it seems like they rushed Partners in Time out, but in my opinion it's rushed in the best kind of way: they just made it short and sweet rather than trying to artificially lengthen it with fetch-quests and the like. If length is a big requirement for you in game purchases, then I'd say look for a used copy.