A Free2Play game, not a Pay2Win!
I have always kept my distance from MMO/RPG games, I've only lightly dabbled in them, none giving me the will to keep playing them. However, POE has done it for me. Compared to some other MMO/RPGs, POE has a bit darker, grittier feel to it.
If you are new to this genre of game, it can be very overwhelming. The passive skill tree is very intimidating and at first will make anyone weak in the knees.
You can literally create thousands of different character builds, if not more.
Give this game a try! Check out the official POE forums! They have plenty of character builds for you to follow and information about races and upcoming events where you can win special items!
Also check out their store for daily deals, cosmetic enhancements, pets and extra storage for your stash!

From the POE website FAQ.

'What does Path of Exile cost to play?'

Path of Exile is 100% free to play, for everyone, forever. Our website will allow the purchase of many in-game perks and aesthetic upgrades, but all of these are completely optional, and players can have a complete, fulfilling gaming experience without spending a penny.

'I still don't understand how it's free to play - what's the catch?'

There is no catch at all, once you download the client you are free to play for as long as you like, with no charge. The purchasable perks do not convey any game-play benefit, but help you create a unique look for your character and its fighting style.