Grim Dawn's definitely not perfect (the game engine frequently looks good but often shows its age, graphic and sound effects are really hit and miss, some skill are much less fun and interesting to use than others) but it's by far the most fun non-online "play at your own pace" ARPG to me.
And the expansion is really good. The new acts have excellent level design (although navigating in some of act 6 is a pain), and the game mechanics expanded across the board. New factions, components, augments, monster infrequents, farming spots, super bosses, and an entirely new end game itemisation because of a brand new block of Epic/Legendary/Set items from 85-100. I'm still playing regularly (at 832 hours apparently.)