It hasn't started yet and the trailer doesn't show much fo the next season so I don't really know, but if you like the gory stuff they have casted John Lithgow as a veteran serial killer who's called the trinity killer because he likes to kill in threes so there probably wil be a lot of that in season 4

Here's a trailer of season 4
http://www.youtube.com/watch?v=PDITTtd1LJk

But ya season 3 had a lot less killing in it, I noticed that too. But I believe season 4 will be good. There is a new killer in Miami called the "Trinity Killer" played by John Lithgow (who can be awesome) and supposedly Lundy (Kieth Carradine) will be back, looking for this new killer. I think it will be better, because season 3 did feel like Dexter was settling down and not up to his old ways as much.

Season 4 seems like its gone back to its creepy, gory roots.
Season 3 wasn't bad, but it was more of a 'character study' season than the other two.

So far, season 4 is far more disturbing considering they've always focused on cold blooded killers, but the 'Trinity killer' is much more of a sick twisted PREDATOR then anything we are used too. This is a much more realistic character, since most REAL serial killers do more than just kill their victims but also assault/torture/rape them for their enjoyment, and because of this he's far more scarier IMO.