I think this brings up an interesting topic regarding games as entertainment vs. games as a form of art or expression. There is of course room for both, but I find they serve a very different purpose.
There are many times, especially in adult life, when you don't want to spend all this energy racking your brain over what needs to be done in a game. Often you can't afford yourself that privilege as an adult. I can certainly tell you from my own experience that more often than not I need my brain-cells to focus on school work or challenges at the work-place. During these times I am more likely to play games in order to be instantly entertained and in order to unwind. This need more often lends itself better to mindless, reflex based games, like racing or scrolling shooters or even highly linear FPS/TPS games than to point and click adventures or Zelda/Pikmin games or turn-based strategy games.
That's not to say I don't need deeper, more thought provoking and challenging experiences to balance out my diet too, but I find myself getting into them more easily when my mind is already relatively at ease, such as on weekends, vacations and so on.
I have no problem with either type of experience as long as the games are honest about what they are trying to deliver. Nothing wrong with some Serious Sam as a side dish to your Morrowind. Nothing wrong with having it the other way around either, in my opinion.
The other thing to remember here is that the more experience you have as a gamer, ie: the more years of gaming you have behind you and the more games you've already completed and mastered, the more new experiences are likely to seem 'simple' or even 'casual' to you. After all, we aren't exactly rewriting the book on gaming with every consecutive console release... Most of the fundamentals are pretty much the same as they were 15-20 years ago.
The same goes for less experienced gamers, who are less likely to have a thorough basic grasp of what a Zelda game or a Metroid game is, since they haven't experienced most of them yet. For them, completing their first or second game of this type probably still constitutes a 'challenge', and as such is probably not their ideal activity for relaxing and unwinding.
The author of this review is obviously not this type of gamer, so the criticism against him is legitimate. But I still think the issue stands as an important one. Regardless of how a game presents itself to the player as being 'casual' or 'hard-core', the subjectivity of these concepts should be taken into account as well.