Offline Single-player has been available for a little while now, just start the game and choose Offline instead of Online, you can even make manual saves.
[Edited by dancoul, 7/29/2016 3:56:08 PM]
Weird.
I didn't see it available yesterday.
I'll try again... maybe my age is starting to get to me :P
also ive had windows 10 since it got released and the game runs very fine for me
I've had gameplay bugs, like the character constantly getting stuck in terrain due to the inability for it to walk up ledges or properly jump.
Using the /escape command throws me right into the very beginning and forces me to kill all the enemies all over again, only to once again get stuck sometime in terrain within several minutes.