I haven't played since season 1, but it wasn't very appealing to me. On the other-hand, I really liked D3.
The monetization is almost entirely for cosmetics. Though, there's an expansion expected to be announced soon.
I don't want to poison your expectations. Go in and see if you like it. The story has some amazing cinematics and the environments have a lot of work put into them. The gameplay generally feels very weighty, which was a design goal since early development.
He/Them
"Am I a butterfly dreaming I'm a man... Or a bowling ball dreaming I'm a plate of sashimi? Never assume that what you see and feel is real!"