At first blush the game won't seem like it's changed much. The lag and desyncs are vastly improved, to the point PoE runs like most other ARPGs. (Although it is extremely sensitive to latency on Lock-step mode.)
The game really shines at higher levels though, IMO. That's when you've built out a skill tree, gotten a good variety of gems, can create whacky combos, have the resources to mod gear, level up Masters, run Maps, mod Maps, etc...
And there's just a wealth of supplemental content now. Shrines with great effects like from Diablo 2. Strong Boxes with random properties. Vaal Maps with random properties. Tormented Spirits. A personal hideout to decorate.
TBH, the game only really took with me after I found a character and build I liked. Then I was hooked. I just got done playing a month long stint of it, gaining several levels on Merciless and starting to dabble in running maps.
I've also come to appreciate the challenge of it. It can get unforgiving at higher levels, where your build, your skills and your timing all are what make the difference between leveling or not. It's got a Dark Souls like challenge for me where things are so ridiculously hard sometimes that, when you actualy win, it really feels like you earned it. On the other hand, a bad build can require a re-roll if you weren't taking things seriously until Cruel difficulty. And I've often been reduced to zerg rushing some story bosses or uniques, xp be damned, just so I can get past it.
All in all, I think it's a game where the appeal builds slower than a game like Diablo 3, but that offers interesting mechanics and a real challenge versus what is now essentially a high speed loot explosion 24/7 in that game.