This. As much as I enjoy the show... it seems to be heading in a series finale direction. It wouldn't be good to continue it to the point where both the writing and the story aren't good anymore.
While it is not listed as being the final season, season 8 starts a bit earlier this year, on June 30th: from http://screencrush.com/dexter-season-8-early-premiere-june/
I love Dexter but the season 7 ending leaves little room for Dexter and co to go on so season 8 should be the final IMO and as for the quality of the show, my own ranking is... 1 4 2 6 3 7 5