Second game seems like more of the same, with some upgraded systems and four player co-op. And I mean that in a good way. The first game is great. I love all the little touches, like how you can shoot a water arrow to create a liquid surface, then either freeze it or electrify it. Or you can shoot a poison cloud and then detonate it with fire. Or electrify a steam cloud. The second game seems to be keeping all of that and adding additional elemental interactions, which should make combat even more of a nightmare than it can be in Original Sin.
Hopefully I can find three friends to play co-op with for it. I've got at least one and possibly two. Just need to find the fourth. Gotta be people who are online a reasonable amount of time though to make it work. Supposedly characters can actually work against each other in the sequel, with varying objectives based on how they align themselves in the game. Sounds like a lot of fun if you've got three friends.
Also, there's apparently a full D&D style separate game included that can be played with five people (one of whom is the dungeon master). I read an article about it and it sounded really cool, and that's coming from someone who has never played D&D.