Fun games are great, but not all games need to be fun. They need to be enjoyable and satisfying, but "fun" isn't a requirement.
"Fun" is such an easy concept to understand compared to "enjoyment", and because the first video games were nothing more than little fun distractions, it's what most people envisage video games as. But if we hang onto this notion of a video game being fun, we will lose sight of what games truly can be. Not only that, because a game 'must also be fun' we are ruining what could otherwise be amazing games, at least in the conservative Triple A space.
That's the problem with the concept of fun, and video games. Fun is very subjective. It's not essential for a video game to be fun to be enjoyable, but it's a very hard line to judge.
This becomes an issue when we start complaining about a new game being too generic. Most of the time the game is either trying to be fun when it shouldn't. Or, it's trying to ride the wave of other games success. What I mean here, is the pervasive requirement for Triple A titles to be "fun" is what makes them boring.