Well, to be entirely honest I think the "problem" is that gaming has gone mainstream and is no longer for the intellectual crowd. It isn't that FPS games MAKE people dumb, it's that they tend to attract dumb people as in the everyman, as they outnumber smarter people, these are what is produced to market to them.
You also have to understand that the everyman wants immediate gratification. Games that start out slow, and have you build up (like RPGs and the like) aren't for them. Nor are numbers and statistics and the like, which is a good part of why gaming stayed firmly in the "smart people" catagory for so long, it took a certain degree of intelligence to play your average RPG (and there was a time when they dominated).
It should also be noted that you have to be able to enjoy dialogue and cut scenes to appreciate Mass Effect, the game definatly starts out slow, and I think the whole section between Eden Prime, and becoming a Spectre drives away a lot of casuals or "immediate gratification" players who basically wanted it to be another space-marine themed shooter.
When it comes to wandering around lost, well I can be honest in saying I can empathize there. Granted there is little excuse to get lost on say the Normandy, but I tend to get somewhat irritated in games where you don't get a clear indication of where to go. I oftentime think that MMORPGs without clear navigation set up are intentionally vague to get people to take longer to do things. There is something to hidden items, mazes, and the like and they are all part of the genere, but say a quest that's like "well go to the alleyway and talk to this guy" when there are like six differant alleyways and the guy is hiding, that tends to rapidly become "unfun".
A lot of stuff people have said before (in this thread even) but still my two cents.
Like it or not the idea of gaming being for "smarter" people are long gone, and honestly I think it will continue to get dumber and dumber in proportion to the number of gamers. Like it or not "smart" people have always been outnumbered, which make us a niche market, even for escapism. Few companies want to cater to a niche market when more money can be made off of the legions of the dull.