Your best free 2 play single player game? (FREE drug inside!!) EDIT: Added a new .GIF. :D

Crossfire (DRM Free)
TF2(Steam)

Some of these

Single Player: Path of Exile

OpenTTD
(needs base game TTD but this is Abandonware so it´s free)

Ascend: Hand of Kul is single player most of the time and it can be pretty fun!

You have to win the game was a really fun surprise.

It feels a lot like the games I played as a kid in the 80s

I'm here for the drugs.

That is all.

cry of fear

Looks like no one liked my free drug. :/

Heroine's quest, Beneath a steel sky, Mechcommander, Mechwarrior 4, recently Lost vikings and so on, there's a lot free single player games that are pretty cool.

Sacred.

And that gif was pretty good. Too bad it last only for a few secs. :D

Team fortress 2 and Rusty Hearts.... loved both games. i still play TF2 once in a while.
also, that thing makes me puke, thanks.

Hmmm... For some reason, that picture didn't work for me. I wonder why?

Free to play AND single player? I can't think of any except for the free games on GOG. Even Path of Exile is multiplayer.

i came for the free drugs :D

Well, the original La-Mulana is great, and it's freeware.
GunGirl 2 is another great metroidvania, you should check it out.
If you're into flash games and RPGs, go for Epic Battle Fantasy 3 and 4, and the Mardek series.
Sunday panzers, if you don't think old graphics are a setback.
If you like bizarre games, you should check "ROM CHECK FAIL" out.
Here's a list of freeware games: Click

All time favorite would have to be: Legend of Zelda Ocarina of Time. Spent hundreds of hours on it back in the day. New favorite single player is: Kingdoms of Amalur: Reckoning

Black Mesa Source

deus ex human revolution the story and gameplay amazing played it and 2nd original war very unique RTS old graphs because is a old game story is nice what i liked about it was is dif from any other rts humans are limited if they die is perm and they gain exp to improve what u put them to do so is in your best interest that they live :P

Best free to play singleplayer game ever

See you in 3 weeks :)

Ragnarok Battle Offline is pretty fun.

Dwarf Fortress

Heroine's Quest: The Herald of Ragnarok is a F2P singleplayer game (point&click adventure made in sorta oldschool style) that recently came to Steam.

It's pretty cool, you should definitelly give it a try. The dialogues are really funny at times, too :)