F2P

It depends what are you looking for. What genres do you like?

I got into Star Wars the Old Republic for a while. It's fun. Loved how it has complete voice overs for all of their characters.

Alien Swarm is a great time killer. get 3 friends to play with you

Dragon Nest

dota2

You can play Neverwinter on Steam, you need at least 30-40h to spend money at all and 50h+ to get something useful.

no more room in hell

War Thunder

The Mighty quest for epic loot,Dota 2,TF2

EQ2 is pretty decent.

Lord of the rings online. It's AWSOME! :D

War Thunder - Ground Forces (tanks) are awesome, planes are fun too.
Robocraft - Build, Drive, Fight - Still in Alpha, but pretty fun. Already greenlit, should be on steam soon™

As said before, Path of Exile is amazing and not p2w at all. I would also recommend Infinity Wars, which is a great TCG.

PoE is genuinely free. Only sells cosmetics, char slots and chest space. All ingame stuff is fair game.

Dude, steam is full of perfect free to play games. CrimeCraft, APB Reloaded, Infinity Wars, Dota 2, Tactical Intervention, ArcheBlade, Super Monday Night Combat and much, much more. Theres a bunch of perfect F2P games outside steam too like Heroes of Newerth, Battlefield Play 4 Free and Battlefield Heroes. Listen to my suggestion, if you want to bring smiles on your face and fun in your life, go and see every Battlefield Hero trailer that is made there on the bfh youtube channel.

Dota 2 and never see light of Sun again

TF2, RiFT and Loadout.

Dota 2!

heroes of newerth.

Dota 2, WarThunder, Hawken, Rift, Path of Exile.

There are. Warzone 2100, doesn't even have an itemshop and is Open Source.

Warthunder !

Black Mesa Source Mod.