I'll sign up for this
I did finish the Witcher because I found it to be a quality game, but a game like Oblivion - well, DuhBlivion can play itself so it doesn't need me. I haven't even finished Mask of the Betrayer to NwN2 (yet), despite having it since release.
The (lack of) quality of games is definitely a factor, but I think it runs deeper then just that.
Sure, the quality and dumping down of games aka Oblivion for example; level scaling, teleportation, huge quest markers and the game making decisions for you in quests, console controls etc .... all that smacks of dumping down a game.
It is because the RPGs since BG2 have begun to become even more mainstream, that means they have to reach a bigger market segment, thus they have to start cater for the lowest denominator to sell more games. This waters down the genre to RPG-lite, because now suddenly it is a crime to be stuck in a game, and actually needing to think. (Who here remembers the "old" adventure games, where puzzles were so difficult that you'd have to wait 2 months for a walk through to be published in a magazine, so you could move on to the next one
).
However this is only part of the equation - we're also "experienced" now. Computer games and computerized entertainment is not a new area anymore - it has matured. This means we as players have "seen it all" so to speak. It is difficult to introduce a plot we haven't seen (Uhh, I have a memory loss and need to discover who I am ....
)
It's like the movie industry - I can't remember the last time I got surprised at a plot-twist in neither a movie nor a computer game (and no, I did not get surprised at SW:KOTOR, that was so obvious a mile away, I mean ... come on
). This makes it more difficult for game producers to find something to draw us in and compete with the games we grew up with purely on the nostalgia factor.
I still install games from the early 90's and play them (thanks DOSBox) to a much higher degree then I do current games, simply because of quality combined with nostalgia, which is difficult to compete with now.
Last I played extensively was Master of Magic - fun fun fun. Even had a "competition" with a guy at work (my age as well) who also played at the same time, and he's not a "gamer" anymore - but these old games still grip him as well.
So while I do think a large part of the reason is dumping down and watering down RPGS (thank you Bethesda), it is also because we've as consumers and players have grown accustomed to the genre. It is hard to come with something new for players like us, so they just target the inexperienced and the twitch gamers that much more who put more emphasis on graphics and fast action gameplay, thus further more dumping down the games.