Well first let me say that this is the first Dragon article I found an interesting read, and enjoyed it.
As far as the flavor goes I gotta chime in with the "options" crowd. Right now I don't think the evil flavor of the warlock should be a forced thing, and as far as the tons of roleplaying possibilities...how would it be any different if the Warlock could choose to make pacts with evil or good. I for one find evil characters disruptive to a game, unless everyone is on the same page...and making a character who does evil to attain his powers just doesn't sit right with me.
I'm wondering from a roleplaying perspective, how exactly does this work. If you have an evil being as your patron, who also supplies your powers, I would assume the being wants something in return? Now you can go the whole Elric/Arioch direction...but even Elric (on more than one occasion) gets slapped down by Arioch for not going with the plan, and eventually the albino turns on him by forsaking chaos. I can't see a player being happy if a DM uses this type of heavy handed technique to enforce the player's price for his powers. Or a player who is willing to relenquish his/her power as they become a hero.
Second thing I'm wondering is why is being the slave of a demon/devil/fay cool or heroic enough to be a primary class? Maybe I don't get the whole "metal" thing (I like hip-hop...not gangsta rap, real hip-hop). Even in other games with this type of vibe...Warhammer, Stormbringer, etc. there is a very real price to pay for this type of power (corruption, mutations, demons turning on you, etc.). Now we don't know enough about the mechanics yet, but if WotC makes this a character with no reprecussions for his/her power I will be sorely dissapointed. It's this, real mechanical drawbacks and risks, that make this type of character interesting. The problems I can see arising with this type of mechanic would be... it will disadvantage the player vs. other spellcasters and would certainly cause strife in anything but an evil PC game.
Elric is an interesting character because he attains Stormbringer and summons Arioch for an understandable motive...love. He is more interesting because he slowly realizes what he's done and unleashed as the world and his personal life suffer the effects of having tilted the world towards chaos. He is a hero because he tries to deny and fight against these forces and in the end is destroyed by them in trying to fix what he has wrought. This is what makes him a hero instead of a villain.
My biggest worry is that the warlock will just be a spellslinger who is evil with no reprecussions or context of what he/she has done for power.
