I certainly don't see a the problem with the Knight. At all. (aside from being kinda stupid, like the warlock, that is. and maybe that loyalty-beyond-death thing reeks of munchkin) Can someone clue me in? To the uh, video-gamey-aspect? Thanks. I just think it would be a boring class to play.
I think the alert has to do with the concept in MMORPGs called "aggro management." Anyone who's played a melee class in an MMORPG has had to deal with it, and D&D has been free of anything like it for most of the new edition, but the Knight has a base ability that's very similar to the effect of MMORPG tanks.
The idea is that the front line combatant, the melee specialist, has the ability to hold the attention of the monster, to focus the monster's attacks on him. Because he has the highest defense and hit points, he can survive the monster's attacks longer, and he protects the others in the party by doing it.
The knight's ability to issue a challenge means that the monster can only target the knight, effectively mirroring those "aggro management" abilities from MMO's.
What that idea fails to realize is that warriors wanting to focus the attacks on themselves pre-dates even D&D (you could argue that chess even has this concept -- you have more pawns, so you want peices to target them). Until recently, there's been no real way for a fighter, paladin, or barbarian to *mechanically* take the attention of the monster in 3e, it's always depended upon the DM role-playing the beast to his ability and the beast's ability to know that the wizards can probably do more damage than the fighters.
The Knight gives us a way to "manage aggro" that didn't exist until then, doing it in a way very much like an MMO's tank does.
I understand where the argument is coming from, but I still think it's a weak argument.