Well I loved them both to death, but not everyone will see them the same of course. I don't know how far you are on 3, but you'll eventually be able to develop social links with the girls. In P4 you can develop them with everyone in your party, and you don't have to worry much about girls getting jealous, and I think that really added a lot to it.

As far as the dungeon goes, you'll sort of be visiting the same place, but instead of just going up/down floor after floor, it has separate areas that represent the person that's stuck in it. It's not quite as big, but I find it more interesting than Tartarus.