Come on, Dexter killing at a place he is known to be at? He doesn't do that. At all.
Part of what I like in Dexter is his level of proficiency when he does his thing. He might make mistakes, of course, he's human, but he never makes mistakes like this. This was a lousy way to make Deb walk in on him as a dramatic ending. She is intelligent, as someone else said in a review: she should've found out by investigating him.
Also, i really don't like how Deb is getting "into" Dex now, but I'm not alone with that..
Another example of horribly lazy writing was when all the crew waited on Dexter before entering the crime scene AND they gave him time alone inside, just because he needed to trash that picture of him.
The stuff happening at the sea and on the ship when Dex was rescued didn't make much sense to me.
Regardless of the lazy writing and plot holes, I still enjoyed the episode (and the season). It would be great to see a new season, but only if some things change. I mean the scenery, and/or half the cast.