However, while I was writing this I took a look at all-time sales charts to see what games are historical best sellers. What I found was interesting:
http://www.giantbomb.com/profile/jagged85/lists/highest-grossing-games-of-all-time-inflation-adjus/89416/http://www.nintendo.co.jp/ir/en/sales/software/ds.htmlhttp://www.the-magicbox.com/Chart-JPPlatinum.shtmlhttp://www.the-magicbox.com/Chart-USPlatinum.shtmlhttp://web.archive.org/web/20090515224703/www.elspa.com/?i=3944http://web.archive.org/web/20060221044930/http://www.ownt.com/qtakes/2003/gamestats/gamestats.shtmhttp://gematsu.com/2014/11/media-create-sales-11314-11914-2This is just a small cross section of articles I could find. Please keep in mind that best selling does not necessarily equate popularity, especially as a few links use highest-grossing quality to determinate "best-selling". However, I still feel the results are interesting and worth a look.
What sticks out to me is that on the majority of charts the best selling games are either arcade games, or games in the progeny of arcade games. Space Invaders, Pac-Man, Street Fighter, Super Mario Bros - but also later Mortal Kombat, later Metroid and Monster Hunter. Most pressingly, however, is the financial success of MMO games. MMO games often use "freemium" tactics to get money out of people and so include a high skill ceiling to increase the time people play. Furthermore, sport games (which can be linked to arcades in that they are closer to a pure 'gameplay' experience rather than an "Experience"), seem to have universal success besides.
These results seem to undermine the assumption that games are becoming more easy: rather it seems that games are becoming more homogenized to create an accessible experience that is enticing to
all (including "hardcore" players). In my experience this is a valid conclusion: games do not necessarily become more 'casual' in-uniform, but rather avoid "risky" ventures to increase the accessibility and sales. This also aligns neatly with the process described in paragraph three: games being made accessible, not easy, by building on popular conventions. For exercise: compare the amount of "Middens" to the amount of "Pokémon".
This conclusion goes against the assumption that video games are becoming "easier". Certainly, more uniform and bland, but this does not equate easier games. The relative appeal of difficulty seems most strongly exemplified in the Souls franchise. Although popularly considered to be a "hard" game, it has done well in sales:
http://www.vgchartz.com/game/31689/demons-souls/http://www.vgchartz.com/game/47349/dark-souls/http://www.vgchartz.com/game/72895/dark-souls-ii/In closing I would like to note that the "maturity" process described in the third paragraph is common for various creative universes. You can see this most broadly portrayed in the Western history via artistic eras: the establishment during classicism, Christian high-tide and the Renaissance, the broadening in baroque, rococo and neo-classicism and the deepening in romanticism and modernism. Afterwards comes the notorious inversion or deconstruction, often unified within post-modernism. If video games experience a similar progression, then I would argue that games like Yume Nikki, Middens, LISA: The Painful RPG, Spec Ops: The Line, Gone Home, UnderTale, Thomas was Alone, Hotline Miami, Killer 7, Drakengard and Portal are the beginning of post-modernism in video games.
* Arguing from a Western perspective.
** I consciously did not conflate the history of PC gaming with that of console gaming or "popular" gaming, as the history of the PC is fairly different until recently (for which we most likely have VALVe to thank). Very early PC games boasted a surprisingly complexity in its "motor compartment", over the pick-up-and-play type of design philosophy common in console gaming. This, in combination of console exclusivity, is the origin of a schism between PC and console gaming. Likewise, PC gaming had an adventure gaming boom, an early FPS boom and RTS boom, as the controls of a PC lend themselves better to these genres. Likewise, due to the more niche appeal of PC gaming, it is more difficult to assign a singular identity to it. Do you choose Monkey Island over Doom? Or Tiberium Sun over Half-Life?