It is basically Diablo 2 with a lot of awesome extra features. And it is the first game I've come across that is actually free to play. There is a cash shop but it's only cosmetic or pets, much like Blizz minus the free leveling.
If you want to try out a spiritual successor to Diablo 2 that has a lot of its own unique features, check this game out. And no I don't work for them or have any stake in this game besides being a player.