I dont like Beth cause they simply make bad games, not cause they aim for the "casual" gamer ~ what ever that now is.
Even by looking at main stream games you can get quality. I have enjoyed quite a lot of main stream media in the past which also include games. Now and then there is nothing bad with that kind of enjoyment. But seriously, all the bugs and stupid design in Oblivion for example proved to me that Bethesda lacks the needed skill to make a game with quality, mainstream or not. level Scaling, broken AI, stupid game design and of course the bugs to name the bigest parts.
Diablo 1 and 2 could be I guess seen as the action RPGs they are as some form of RPG for the masses. So? I love it, still. Its a great game. But its not as buged like games from Bethesda and thinking about what they wanted to achieve with Diablo its gameplay makes much sense.
Bethesda also doesnt even care much about its own fanbase (see the changes from the Dagerfall to Morrowind and now Oblivion). Thats why I dont like them.