if you're a fat, unwashed, unhealthy, depressed, social outcast, social retard etc. etc., nothing will be fun. you'll just cry how nothing compares to fallout 2/ bg2 etc. etc.
you can play the best game in the world, while feeling like shit and you'll get mildly entertained at best, and at the same time a casual healthy normalfag sheltered faggot permanoob pleb4life is playing some shit streamlined piece of garbage and enjoying it 1000x times more.
so if you seek fun in games, my advice is to get your mental and physical health to decent levels.
most fun I've had was playing alien vs predator with friends, we could only play at a net cafe, only on friday coz we'd skip classes, 2 of us had retarded parents who didn't allow any fun.
the game had a lot of depth, aliens, predators and marines were completely different, and in avp2 they all had different classes.
games are fun when there's a good balance of effort/reward/replayability. knowing the time u spend on it will improve you for the future.
also a good story which makes you want to see what happens in the next chapter and making you feel like a protagonist.