I can never get myself to finish a game. Help!

I played many games. I only finished one and that is pokemon emerald. But whatever game i play now i don't finish, i just left AC Syndicate even though i enjoyed it.... But i can keep playing multiplayer games like bf1 and bf4.

Do you know any good games that will keep me playing till the end, possibly something like AC,MGS, or an action adventure game? I'm on PC BTW

Thanks for any reply, I appreciate that you're​ taking your time to help me!