Well, I think I can speak on behalf of myself, Fing, and Kalinaf and say yes. The gameplay has changed quite a bit, espicially for established players on the higher difficulty settings (Nightmare, Hell) but they have definately added enough new things to keep me interested. For those who don't know what's new:
New "Elite" weapons (the strongest in the game)
New Set and Unique items (you can now have partial set bonuses, which makes having even just 2 or 3 pieces of a given set worthwhile)
Armor can now have sockets
Runes (they can be insereted into socketed items and have unique attributes. And if some are insereted in a specific order into specific items, you can come out with a very very powerful item)
Jewels (Like gems, but with multiple attributes that are more like magic items that can be put into normal items)
The new Act 5 (Definately the most fun act of all)
If anyone who has the expansion wants to play, myself, Fing, and Kal always play in Game/Pass: pgoh/pgoh
If the game isn't up, start it, chances are one of us will join you at some point