Personally, I don't approach this topic as "gaming has been dumbed down" anymore. It's too general of a statement. This isn't a monolithic playerbase. Every game/franchise/company has their own set of fans with different tolerances for complexity. At best one can make an argument that an existing company has made a move from a more complex to less complex for sake of expanding their audience, creating a feeling of betrayal from the a subsection of their fanbase that specifically preferred their games for sake of complexity all else be damned.
But that's something you review on case by case basis. With added dose of "did that complexity really do something for the quality of that game?" considerations.
For example, ME1 --> 2. Examine simplification of the skill system and the inventory system. Quite frankly, when comparing finished product to finished product, nothing of value was lost. ME1 item system was mindless. Mindless item pick ups, mindless progression, illusion of choice. The only thing that was even barely interesting about the ME1 item system was were weapon/armor mods, and it pretty much came down add damage, subtract heat or stack regeneration to reduce downtime. Skill system was similar as well - the only choices of consequence were "did I pick up my class's uber skill" followed by "did I pick up Persuade/Intimidate?"
Yes, theoretically, ME1 had greater complexity. Practically, almost no complexity was lost. Yes, ME2 could have attempted to fix all of that and make the existing complexity into real choices. Practically, Bioware is horrible at balancing the choices they give, so I am glad they acknowledged their limits and simplified the system to something within their capabilities to create real choices in. The result of that decision? ME2 trimmed away the rot, iterated on making the classes feel distinct, powers more balanced, core gameplay more interesting. And now that they solidified their basics, in ME3 they are bringing what looks like useful complexity (look the promised changes up: http://masseffect.wikia.com/wiki/Mass_Effect_3).
So, in other words - the dumbed down argument needs more support beyond wounded cries of hipsteresque "it's popular now it sucks." For one, I would love to see evidence that the casual overflow is legitimately strangling the numbers/quality of complex games. For two, it would be great to see examples of truly great games where one could truly make the argument that the simplification in terms of complexity was followed by simplification in terms of game depth. I know UT is one such example, and I heard something about Civilization? Etc., etc.
