what are some single-player games with alot of replayability?

Probably Minecraft. If you play the game with your friends then it will never get old.

Assassin's Creed 2 and 4 are pretty replayable for me

Fighting games like Street Fighter or Mortal Kombat. After you get good with one character you can switch to another to learn a new moveset and strategy.

Resident Evil 4, really loved this game

My favorites are RDR2 and Witcher 3. W3 is kind of like Skyrim, play it over 10 times and you will still discover new stuff. Red Dead was more of a 1-2 time play through type of game. But never gets old when you see a lady being kidnapped, kill the... "kidnapper"? And then kidnap her yourself.

which game do you recommend for a computer without a video card

Aside from Fallout/Skyrim which you already mentioned, and Witcher 3/Red Dead Redemption 2/Dragon Age Origins and Inquisition which were mentioned above, the Mass Effect series were pretty sweet. GTAs not too bad too (San Andreas, IV and V mostly. Vice City was nice too but too short.) and maybe something like Grim Dawn or Borderlands 2/3.

EDIT: I forgot Nier: Automata!

I've been playing XCOM 2 lately and really digging it. I also picked up Humankind and was enjoying that as well, a nice Civ-like game.