I still haven't watched Season 4.
I got about 3 episodes in then never watched anymore, although it was mainly due to a number of other shows that were appearing at the time (and the fact I'd just become a father to twin boys so my time was limited).
I had wondered how the season went but never went back, and the show then got cancelled so I missed out. Would probably catch it again if I could. The first season was great though.
I heard Tim whats-his-name did want to introduce lots of new characters each season and only a few would carry over each subsequent season, but was ordered by the powers that be to retain the core cast.