A bit of a cross between the two really. Some episodes are really good and have an X-Files feel to them.
It's nowhere near as teeny as some of the CW stuff -- ie Smallville.
Season Three was a mixed bag -- but I don't think the writers' strike helped.
Season One started off almost as a monster of the week-type series but, as the mythology grew through the second half of s1 and s2 it got a lot better.