This is a great question. A college thesis could be produced by someone intense enough to take the subject on.
For me, games are not fun anymore because the industry is not fun anymore. Having worked in the games press, I've become privy to the observations about the industry that shatter the hobby's mystique and make it as dirty, grimy and self serving as all other industries. Additionally, the conversations behind closed doors about what should be discussed and what should be avoided corrupted my ability to view video games through the lens of my youth.
I think that for 'fun', the indie scene is the place to go (although even that arena is growing increasingly cynical between manufacturer regulations, industry divisions and backbiting). Shovel Knight is practically a perfect game of its type, well tested and with enough variety and replayability to take me back to the days when I could just lose myself in the thing without thinking about all of that stuff.
Because of the information we have available to us these days, I find myself more willing to embrace games like Yakuza, Ninja Gaiden, Devil May Cry and Dark Souls, where there is a specific concept and goes after that to the exclusion of outside influences. Hideki Kamiya is an angry artist, but he is concerned with bringing his vision to life. There's no proselytizing in Devil May Cry or Bayonetta. Just that elusive and irreverent 'fun' which the industry seems so incapable of committing to.
I also think that the industry (at least in the West) is geared more towards shared experiences-multiplayer, Twitch, etc. In Japan, theme is still king.
My thoughts are, admittedly, scattered on this subject. It's a pretty massive issue and the more I think about it, the more depressed I get and the more old I feel.