Funnily enough, original characters don't bother me at all. I guess because there are no rules to follow with them and no one can read it and say 'Well, X would never do that!'.
Although, I guess they could if it was a long story and a character pattern had been established that was worked against.
But, generally speaking, you have a much freer hand and less to worry about.
So, I'm curious - what is it about original characters that you've found restrictive?
LabRat