The lines for Millennium Force are still long. Unless you make use of the FastPass (I think that's what it is) stuff, which lets you get a pass for a much shorter line once a day. Typically we would wait 15 minutes with FastPass, an hour without.
We also stay in the park at the Breakers, which lets us in an hour early. First ride is the MF.
In general there are fewer people for Halloweekends. If you really want short lines, I'm led to understand that July 4th is the day to go.