Given an older quote of mine from the original VG thread, I might just have to agree with that sentiment!
"If the game has levels that can be beaten in 15 minutes or less on average, even if it has 100+ levels, it's probably a casual game, because you can pick it up, play it for a bit, and put it away, as a little fun distraction between your important stuff, instead of having to set aside a more significant amount of time to play.
Interestingly, this means that many FPSes out there could qualify, by my definitions, as casual games. Especially the multiplayer stuff. And those are considered by most to be hardcore games."