I had exactly the same reaction to season two. About halfway through, I was talking to one of my friends about how disappointed we were, and I was thinking about not watching it anymore. Then there was one awesome scene in which Dexter headbutted Doakes, in which I completely saw where the season was going, and it was a rocket ride. I was practically jumping up and down waiting for my friend to get the finale on ITunes, at which point we agreed the second season might actually be better than the first.
That's one reason I'm willing to give the show so much more rope this year. I agree with some of the criticisms I see about the stories so far, but that's how I felt at this point in season two, so I've decided to have faith in their abilities this time around.