>I may watch it despite how much it apparently falls off

The first three seasons of Dexter each close a story off. Think of how Red Dragon/Silence of the Lambs/Hannibal are all movies in the same series, but each tells its own completed story.

You can easily watch the first season of Dexter and get a complete story told, no need to go forward if you don't want to. Same with watching the second season, and again with the third season. It's only when we get to the end of the fourth season that there becomes unresolved storylines, which is why the fifth season takes place right away afterwards (like how Game of Thrones works).

I think that's one of many reasons why Game of Thrones fell so hard. It's one big long movie, like if Return of the King was a lacklustre disappointment after the well-received Fellowship/Two Towers.