Strangely, I can't exactly picture Aragorn, or any other character in the books. While I am reading it, pictures do form in my mind, but not in ways that I can explain, or even remember later on. But as I afore said, Viggo was not what I consider a very good Aragorn.
But, I think that if the he had been better portrayed by the movie makers, he would have done fine. So even though I don't think he looked like Aragorn, he could have been made to seem to look more like Aragorn... if that makes any sense.