Diablo 2 didn't have pets. Diablo 2 didn't let you have more than one skill tree. Diablo 2 didn't really have a sense of adventure, you were just ported to the next town after you defeated the boss of the first.
And yes the rest is nearly exactly the same with some small tweaks to improve gameplay. To me this game seems like a mix between Dugeon Siege and Diablo but leaning more towards Diablo. But as I've said before a lot of people like this game because it's like Diablo 2. Sometimes it's good to just stick with what works, it's enjoyable and they didn't want to fuck that up.
I'm all for innovation but a game doesn't always need to be radically different from it's predecessors.