Personally, I think the term "fun" is overused. For one, its so vague it means literally nothing. Its like "cool", or "nice". Also, it gets to the idea that all video games HAVE to be fun, all the time, which is not true. They have to be engaging, but not really fun. Is Spec Ops fun? How about Last of Us? Silent Hill? Dear Esther? Walking Dead? We use the word like it was some sort of holy grail, something no game should ever ship without, when in fact its an antiquated necessity ever since video games stop being seen as mere toys on the TV.
Appealing to a mass audience is not the issue with "fun". On the contrary: Mass audience appeal result in games that are bland, but they are too bland to even go against the holy grail of "FUN". You are never going to find a game targeted to a mass market to engage people in any other way that is not "look at all this fun!... excitement!... explosions!". That was the reason with RE6, a game that had 6 playable characters to satisfy the RE4 fan and the Gears fan at the same time; or Dead Space 3, a game that largely abandoned survival horror in favor of "shooter with monsters" and included co-op because people complained it was "too scary" and therefore "not fun enough". The issue with "fun" (that, at least, the previous GTA had) is that it saturated the game with gritty mood to the point fun becomes irrelevant. Some games need to have serious topics, but in the case of GTA, the gameplay depends on randomness and antick displays of violence and chaos. When it juxtaposed it with the moody story it tried to create, the result was a game that feels disconnected.