I am going to start this post off by saying this is purely my opinion.
I am also going to try and stay constructive so I ask everyone else do the same.
Now then, in my eyes when a sequel is released in the gaming industry in most cases they keep the core mechanics, especially if it is what made the game unique.
1. If it isn't broken don't fix it, improve it.
Path of Exile has a bunch of stuff that was in Diablo 2 but instead of just copying it they improved it.
Magic find: Path of exile has two MF stats, rarity increase and quantity increase. I feel these are self explanitory. The stats are seperate entities the player can choose which they want to prioritize.
Bartering system: PoE has taken the barter system to a whole new level. There is no gold in this game, even the vendors bargain using things like ID scrolls.
Player bartering: In D2 sojs and pskulls were used as bartering tools, PoE added there own types of bartering tools for example, they have a bunch of different orbs that do different things.
Orb examples:
Orb of Chance: this orb is used on a white item and makes it one of the following: Magic,Rare,Unique.
Orb of Alchemy: this orb turns a white item into a rare item.
Chaos Orb: This orb re rolls the modifiers on a rare item.
Anyway there are a ton of different orbs and players have assigned them all certain values, they serve as a basis for trading between players.
Gearing yourself: As you can see above these orbs make the game much more fun, if you get an awesome item but the modifiers are bad just use a chaos orb and re roll it. Find a white item? Turn it into a rare. The most fun part about this game is how versatile it is. You do not even need to trade with other players however it is still a good idea to.
CUSTOMIZATION: Path of Exile has taken customization to the next level.
I introduce to you, the passive skill tree.
http://www.pathofexile.com/passive-skill-tree/Now this might seem overwhelming at first however allow me to explain...
See those orbs in the middle with faces, those are where different classes start in this tree.
All classes share this passive tree, being a certain class puts you closer to certain abilities.
For example. starting at the top puts you closer to alot of int based skills where as using a class that starts at the bottom puts you closer to strength.
Now you might say "well what if i mess up do i need to re roll?" Not really. There is another orb called "Orb of Regret" it allows you to undo one skill point per orb of regret. Other people might say "well then there is no customization people can just keep redoing there build so no point in re rolling" To this i say these orbs are not cheap, youn can redo your entire tree if you want but it will cost you alot. Orbs of regret are more used for minor adjustments or mistakes.
Next on customization... All classes have no abilities, your abilities are based on gems you find which you socket into your armor. these gems are based on your stats for example..
Blue gems = Int
Red gems = Str
Green gems = Dex
to use these gems you need to be a certain level and have the enough of the stat needed to use it. These gems allow you to further customize your character with any ability you want.
Want a bow and arrow necro? go right ahead.
Chat: In D2 you had to go to a chat channel to talk, in PoE there is global chat. You can talk or advirtise your gear to anyone who is in the same difficulty as you. This is a huge improvement because you can be mfing or leveling while getting your trade goods out there.
Quality on items: Remember in D2 how you would hunt for those 6 socket weapons or 4 socket armors hoping for a good +defense % roll? PoE has that as well. Its called quality. Some items will spawn with anywhere from 0-20% quality. The idea is that once you find a good quality item to keep re rolling it until it has the mods you want. There are also stones you can use to up an items quality.
Uniques: D2 has a lot of uniques at lower levels that people would use even at lvl 99. Chancies for example. PoE also has good low lvl uniques that are useful at higher levels.
Uniques 2: Each unique has a set role you could say. They are rolled with stats that fit that roll. Unlike d3 where a barb item might be rolled with int.
Leveling: Just like in D2 where only the hardcore would get to level 99, PoE currently has 100 levels and it is the same here, it will take forever to hit 100. But to hardcore players who want it the feeling of satisfaction will be there.
Besides having a huge exp curve in the later difficulties you also lose experience when you die. So like i said this is for the hardcore, but it is an aspect we all enjoyed and its here to stay.