They're really overpriced (42$ for 1 armor set...) and there are some loot crates too, but at least they're mostly cosmetic and none of that p2w bullshit some other games have. There are some convenience purchases (trading is really annoying if you don't have a premium stash tab, and the crafting mats & map storage helps too), but it's not as restrictive as to be unable to play due to inventory limitations. Many people play on the no-trade option too (SSF) and then you could say you don't need the trading tab at all.
Let's see how they fare after Tencent bought them out, but I reckon Tencent bought LOL as well and LOL is doing fine in that department (no p2w either).
Unfortunately the praise-worthy f2p games are so few, far & between the blatant cash grabs trying to milk you at every step.
I think POE rose due to Diablo3 being in maintenance mode and nothing really new being added to it, so action RPG fans moved on, however POE has much more complicated character class & progression system than Diablo 3 so it's much less "noob friendly". It can be it's biggest advantage or disadvantage, depending what does the player want from a game. But definitely it's a well crafted game, none of these cheap clones of popular franchises.