I find myself coming back to this game more often than any other game (example Minecraft).
It has been the game that has destroyed so many of my friendships, as well as made me replay the story multiple times.
If you a a mean person, with a broken sense of humor (broken based on today's standards) and have no friends, the singleplayer is PERFECT for you!
if you do have friends and wanna get rid of them, this game is also great for you!
If you want to forget about reality and you have too much free time on your hands, speedrunning the singleplayer is for you!