is the single player campaign good enough?
The game doesn't truly begin until you finish campaign and that was true with D1, but the single player campaign is truly great, I enjoyed the story. I'm a continuing player from D1 and D2 is good at making you feel the struggle (environments are breathtaking) but once you hit requirements to go do the first Raid, you're interest will start waning as you realize the purpose of the "the grind" is to get max power level and loot which currently serves no purpose. Correction, it'll get you ready for the expansion.
TLDR: It'll hold your attention for the first month, beyond that you start searching for alternatives.