The phrase "uninteresting characters" means that the characters in a book, movie, or play are not engaging or captivating. They lack uniqueness or depth, making them boring or dull to the audience. Full definition
Chris Hemsworth is a likable, charismatic actor, but his Thor, from the start, has been the dullest, most uninteresting character in the Marvel Cinematic Universe. (lights-camera-jackson.com)
Uninteresting characters after Altair & Ezio. (thesixthaxis.com)
I have had the most massive grudge against Square Enix spending all their time at that time making Final Fantasy games about Lightning, the most uninteresting characters Final Fantasy has ever SEEN in my opinion. (gamerassaultweekly.com)