Path of Exile is a free to play action-RPG game similar in style to the Diablo franchise. A game focused on deep customization through using unique feeling characters. This is all offered for free, with in-game purchases available for cosmetic items and improved inventory storage.
Pro Completely free to download and play without falling behind
Everything is completely free to download and play, and you won't fall behind if you choose to play for free. However, you can buy cosmetic items (items that will make your character and skills look different) and stash tabs (they allow you to hold more items that you're not using) in order to support the company.
Pro Fast and furious gameplay
Path of Exile is generally about one thing: killing lots of things, and killing them insanely fast. The game only gets faster as you get more skilled and further along in levels, which makes it incredibly hard to become bored.
As you level up, more skills become available to you in the form of active skills and support skills. Active skills are exactly what they sound like - skills that are able to be used. For example: Spectral Throw will throw a ghostly version of your weapon and is available at level 1, while Earthquake will make you smash the ground, causing it to erupt a moment later, but is only available at level 28.
Support gems grant different effects to your skills. There's basic things like Faster Attacks which simply makes you attack faster, and more complex mechanics like Cast on Critical Strike which allows you to cast a linked spell every time you critically strike with your attack.
As you grow in levels, you can link your skills together in more interesting ways, leading to much more carnage and destruction.
Con Graphics are a little lackluster
While not the worst, the graphics do not really stand out as polished and look somewhat dated. While it does fit within theme of being a grimy universe with many foul creatures, it does not compare to many AAA dungeon crawlers out there such as Diablo III.