For me, the best part of playing Path of Exile has been hanging out and chatting with my friend. I can't really lay the credit for that at the feet of the game, except in the sense that it was the catalyst. I should probably do this sort of thing more often. I guess I'm just so used to being the only person in my social circle to be awake that I forget it's an option.
Leaving aside the social aspect of the game (which, seeing as how we used 3rd party software to voice chat, seems fair), my main thought is that I really should play Diablo 2 someday. That's not a dig on Path of Exile, it's simply becoming clear that the Diablo series (and Diablo 2 is the one I hear most frequently called out for this) is so widely influential that when I play a game like Path of Exile or Torchlight II or, hell, Borderlands, it would be nice to know what was borrowed and what was original.
The core of this game is pretty solid. You control a fantasy character from a third-person overhead view and can map powers to various buttons. The character I'm playing now has a double-strike on the left mouse, lightning field on the middle mouse, and flaming teleport dash on the right mouse, so cut up powerful enemies by right-clicking on them, disperse crowds of weaker enemies by middle-clicking on the ground in front of me, and escape from or advance into combat by right clicking the appropriate part of the environment.
This creates an almost hypnotic rhythm of play. See an enemy, click, see more enemies click a lot, enemies gone, sort through loot. I could probably play it for weeks, easy. It's not very deep, but it is just intellectually engaging enough that that doesn't matter.