At it's core , Path of exile is a good game. It contains all of the qualities people look for in this type of rpg. That being said, it is an exercise in frustration if you do not follow it's spacific formula for success.
The most glaring problem with the game is its poor net code. You will die to desync in this game. You must train yourself to constantly be on guard for the signs that your character is not synced and try your best to mitigate it's effects. This makes hardcore leagues and races tedious and saps the fun from them. No other game of this type, or any type for that matter has ever been this bad for me. The devs are aware of this problem, but have been unable to make any progress toward a fix.
If you decide to play softcore, or get sent there from hardcore, you will deal with experience loss on death. The devs are fully aware that desync exists, they can not fix it, yet they leave a punishment mechanic in game if you die, when they can not differentiate between a deserved death, and one caused by thier poor engine. At higher levels this can mean hours of grinding wiped clean through no fault of your own.
There is no pay to win mechanic in this game. You must earn everything you need to progress through gameplay. The drop rates are well tuned, but the chance of getting anything you can actually use are so low, that you are forced to trade in order to progress once you get to the end game. This is true for a lot of games, but the problem here is you have to either watch tradechat, or use third party sites to obtain the gear that does not drop for you normally. This is time consuming and tedious.
The learning curve in this game is pretty big. There are literally millions of builds that you can end up with as you traverse through the game, but many of those builds will not be viable as you close on the endgame. The most basic rule you must follow if you want to succeed in this game is, Research, Research, Research. If you just start the game , and do not do research, it is very likely you will end up at a progression wall you can not climb. In most other games, this is not an issue, as you can take the lessons you learned, buy a respec token or whatever and fix the problems with your build. This is not the case in this game. Respecing is expensive, (in game money, you can not buy a respec for real money) So you learn that you are better off just shelving your character and starting over from scratch. with no variation in the game story, it becomes just a borefest to get back to where you were previously with your new build.
This game would get an enthusiastic Thumbs up from me if it were not for the above issues. As it stands now, I would suggest to anyone reading this to research what desync is if they do not know, and see if they have the ability to mitigate it enough for the game to be enjoyable. If you decide you can live with it, I suggest you do some deep research on the skill tree and game mechanics, before you even start playing. You can find a lot of cookie cutter builds on the forums if you do not want to theorycraft yourself.
If it were not for the desync/death punishment mechanic I would endorse this game to anyone who loved Diablo 2. Instead I will have to vote thumbs down on this, as the issues I listed will not be fixed, and just cause too much frustration as you close in on your end game goals.