Discussion: are trilogies* a bad idea at this point?

Because I can't think of a recent (past 15 years) planned-as-a-trilogy series that didn't at best end with disappointment and at worst utter disillusionment

* LOTR, movies or books, do not count, as in both cases the author/filmmakers made them as a single unit and released them over time

Like, let's look at trilogies:

Batman (Nolan): good first entry, legendary second, middling third
Mass Effect: great first, great second, great third but with an abominable ending
Star Wars: great first, great second, abominable third

(obvs I'm referring to the Star Wars sequels above)