I think that if you already own TS2 and your system will run it you should definitely give it a try again.
But there are differences, if you can get over the graphics in the game and the limitations of build mode & CAS (outfits in TS2 come with shoes already attached, hats are on hair, etc) .... for me the things that sims do together and all of the animations being so detailed is amazing and I still enjoy it.
I love playing Open-For-Business and having a beauty salon to de-fuglify the townies in a gameplay function, which to me is much more satisfying than just popping them into CAS in TS4 and making them over. With TS2 you have the randomized event of failing at making them over, and that sim will be mad at you, also their look will remain that way until you convince them to let you make them over again. It's comical and I really enjoy it.
I like how kids play together.
But needs decay a lot faster, it's harder to build up relationships, you need to maintain relationships for promotions, etc. It's harder. And, like others have said, it's harder to play rotationally. I'm not a rotational player so that didn't ever bother.
But, I also miss things when I'm playing TS2 compared to TS4, mainly build type stuff ..... shrinking/enlarging objects, raising or lower objects, freely moving wall items, etc.