I started playing in Harbinger, and after hearing everyone's dislike of Harbinger as a league, one of the most confusing things to me was how well-liked Perandus was. The two leagues have the same core gameplay loop: fight some extra faceless mobs that take too long to spawn, kill your framerate, and drop special currency in annoyingly small denominations that's tedious to pick up. All Perandus has over Harbinger is a fat guy that spawns every few maps and offers you free loot in exchange for that annoying-to-pick-up currency, and sometimes that free loot is T1 rares at unreasonably low prices.
No real difference in the core gameplay, but a fat guy that offers you free shit is apparently the difference between a great league and "garbinger". What makes a league "not boring" or "not too complicated" to people is just the amount of free shit they get, not the actual simplicity or complexity of the mechanics involved.