I'm really not sure on anything yet. Race/gender will probably be left up in the air until I either get to play around with character creation or figure out if I'm aiming for a specific romance my first playthrough. From what I've read of the abilities I want a rogue, but since the mage party members look the least exciting to me and I really like both Sera and Varric, I'm considering going mage my first playthrough and with Mage!Quizzy/Sera/Varric/rotating-warrior-slot being my primary party.
Roleplay-wise, I'm ever so slightly leaning towards being pragmatic in the beginning and, if I see the proper oppurtuinity, jumping off the slippery slope at some point to become more and more evil (and possibly paranoid) as I go. Assuming I go with human mage, I can see my character as really disliking the circle system, and becoming more and more critical of the Templars as they fight them. And then becoming more and more critical of the Chantry for allowing this to happen. And moving from there into the "no one but me can be trusted with power" idea, because all factions are obviously abusing it, and will use it to oppress mages. That'll probably just become rhetoric at some point, assuming I can make it clear I don't care for the mages and I'm just looking out for myself. Bonus points if I can pull off some nice hypocritical actions somewhere along the line.
Otherwise, if I don't find a properly vicious choice to make, I may roleplay as someone who really was not prepared for the level of responsibility now thrust upon them, and would much rather just be following someone's orders somewhere. I'm thinking this would eventually develop into either an emotional wreck (angry or depressed all the time) or possibly falling into a sort of shell-shocked detachment -- after all, if I've already screwed up so many times, what's one more? This character might actually end up taking primarily good choices, especially if they are self-sacrificing, and would almost certainly want to go out in a blaze of glory at some point before the wars were over and they'd actually have time to confront the choices they made.
Actually, the more I think about, these could both stem from the same human mage character. Initially I didn't have a problem with the Circle, but I fell in with one of the more radical groups due to a sense of loyalty to my friends or a charismatic leader. When the war broke out I mostly followed their lead, rationalizing that it really wasn't my fault I kept having to fight and kill the Templars -- they kept pursuing us, and I couldn't just abandon my friends. And I wasn't making the decisions, I was just following their lead, so it's not like I really did anything wrong. But then everyone I followed died at the peace summit, and I'm suddenly thrust into a position of responsibility I really can't handle. At this point I'd have to see how the beginning of the game plays out, to see if my character will shirk from their growing power and influence, and thus fall into the type of character described in paragraph 2, or realize that they liked thier freedom/power and take more and more morally questionable actions in an attempt to secure it(after all, your ability to close rifts is only important so long as there are rifts, and you don't want to set someone else up to stab you in the back once the wars are finished). Of course, both of these characterizations will depend upon what options I have in the game, particularily conversation-wise, as most major decisions can be rationalized somehow. In this regard, being emotionally unstable will likely be much easier to play, given that there's usually an appropriately angry response to everything.
Side note: If there's an option to become an abomination for power, I'm totally taking it. Hopefully more of an Anders "slowly consumed by the emotion/ideal" one and less of a Wynne "holy carp there actually are good Fade Spirits apparently" one.