I believe that the plan was to 'reboot' the franchise now that Arnold is no longer involved in politics. He was very vocal about the last couple of movies being bad and was a strong proponent on getting new movies made. I think I read somewhere that the plan was a trilogy of sorts starting with the latest one, but not too long ago I read that some of the cast didn't want to reprise their roles or had conflicting commitments which is a shame as I thought the latest one was good. You'll get people who nitpick and disagree, but you cant please everyone.
My favorite of the movies is #2. My view on it is that it allows us to see both sides of the coin. How evolution and in turn how machines can become to big for their casings as well as used to help (Reprogrammed T-800). How we as humans are evolving to a point where we think we are doing mankind good, but we can also be leading the way to our destruction. I really wish that the TV series (Sarah Connor Chronicles) lasted longer.