Big fan of this series. I feel like it is what Resident Evil should have evolved into. Lots of scary and intense parts, and plenty of shooting. Plus it delves into the psychological aspect of Isaac pretty heavily in the second, which makes the unfolding of the story fantastic. I also have to admit that Ellie, the girl from part 2, is probably one of the most endearing, and probably one of my favorite, non-RPG characters I've encountered.
This new game is going to feature drop-in/out co-op, much like Resident Evil 6. Apparently this was their plan from the beginning, but couldn't implement it until this one. This game is looking like it'll be a must-buy for me.