I got my compy of MW a couple of weeks ago and I've only played apprentice games so far (my first full game tomorrow, hopefuly).
I have a friend who is naturally very aggressive (in gaming) and he defeated 3 out of 3 by just rushing me right from the start and keepin up the pressure. I feel really lost in that kind of situation - we played warlock vs. beastmaster (him being warlock), priestess vs. wizard and beastmaster vs. wizard (me being wizard in the last two) and he just got me every time by pushing onward and on on and on till I died
Although the priestess/wizard match was the closest and longest, he still got me in the end.

Now, the thing is I've never been good at being straight-in-your-face-aggressive in games, be it video games, board games or whatever - somehow I'm more of the defensive-waiting-for-an-opening kind of guy.
Maybe it's just the apprentice mode with it's small arena and limited spells, but I really felt helpless against his aggressiveness. :O

[Note: I played a couple of apprentice games before playing with him, he never played MW in his life]

So - what do you do against extra aggressive players?