I've played POE for quite a while now with three characters at lvl 50, one Scion, one Witch, and one Ranger.
The Good: The character customization is good, in fact it's very good. (except the whole gender lock thing) The huge amount of passives in the passive skill tree and the sizable amount of skills you can mix and match really allows you to play a character you want to play. Nothing is more satisfying than thinking up a play-style for a character then bringing it to life, and when your build works, you can't help but feel almost proud of your own creation.
The Bad: Unfortunately, the game is imbalanced with casters and warrior type characters coming out on top and dexterity based characters left in the dust. This imbalance is mostly due to the fact dex type characters need to spec damage and survivability, and I quite often found with my ranger that I was getting 1 shot a lot if something hit, and that my damage was severely lacking. If you hit hard, you die, if you don't die, you don't hit hard. My Scion does a lot more damage than my ranger, and is much tankier.
You may be able to make a build you love and play the way you want but it might not actually work, and you will be frustrated to hit lvl 45 and realize your character just isn't able to keep up. This is made even more frustrating because the game has no full passive tree respec option, meaning if you mess up, you re-roll another character, or you waste time farming orbs.
The Good: Because you can make your own character in mind, combat is super fun. Skills are also very flashy looking, and have a good sound design that gives the feeling of oomph whenever you hit a devastating hit.
The Bad: For me, the combat is often interrupted by a huge lag spike that often gets me killed. This is extremely frustrating. I know it is not my computer, but the server, and this needs to be addressed. Combat also tends to be repetitive and some bosses are just stupid to play against. This often gives the game a very inconsistent skill curve, where you just mow down 75% of enemies, then get 2 shot by other monsters. I often found myself realizing I was not tanky enough and having to level a few more times to get tankier in the passive skill tree.
The Good: The world has much hidden lore that is well written, and the voice acting is decent for the NPCs, and very good for the player with some select NPCs, like Captain Fairgraves. The story is indeed dark, and reading about things gives context to what is happening and makes the atmosphere more enjoyable.
The Bad: Horrible main story. It basically doesn't exist. A lot of characters aren't even explained well, and there feels like there is so much more that should be included in the game. This is a problem because when you fight a boss it often feels like your just trying to get to a path, and the boss is just blocking your way versus the boss being something important for you to deal with.
The Good: Fast leveling without feeling too fast. Leveling is always exciting.
The Bad: Leveling get's a lot slower and is scaled, meaning although I'd love to help my lower lvled friends, I don't really get anything out of it.
The Good: No Gold, helps limit inflation.
The Bad: No real effective way of selling to a wide audience.
Overall Path Of Exile is a good game at it's core, but feels a bit lacking. It is short, has no real story, and is often imbalanced. But did I have fun playing the game? Yes, tons. Would I recommend this game to others? Yes for sure. This is a game that is f2p but has p2p quality of combat and customization, but f2p everything else really. However, the game is new, and the devs are adding new content all the time. So if you like kicking ass, if you like playing what YOU want to play and not being told what to play or how to play, then this is the game for you. Just don't expect a good story, and do expect some occasional lag spiking that will get you killed.
As a personal note, my favourite character is my scion. I built her mainly STR, with some DEX tossed in, and some INT tossed in. I currently use Spectral Throw, Leap Slam, Cyclone (so fun this skill), Frenzy, and Flicker Strike, with some defensive skills (Molten Shield). I'm always jumping around the screen shredding through enemies and moving around, very fun.