These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Blue's Clues
Accidental Innuendo: We never find out what the book Steve reads in one episode (the book is called "A Really Great Book"), and he's very into it...what is that book about!?
Crowning Music of Awesome: You best believe it. And even if you don't much care for music aimed at the six-and-under set, you've got to admit that the show's full of Earworms. The show's theme tune is a good example, and the "Glasses" song from "Magenta Gets Glasses." There was also the "Puppyville" song in Meet Blue's Baby Brother. "Look at all these puppies, this must be Puppyville!"
Fridge Horror: In a later episode about patience, Joe helps Periwinkle — the neighbor cat — be patient while waiting for a bird's egg to hatch.
To be fair, his best friend from the city is a bird.
What's going to happen to Mailbox when the United States Postal Service finally shuts down? I doubt Steve and Joe would just get rid of him, but there's not going to be much for him to do other than be a big purple lawn ornament...
Les Yay: A lot of adult watchers think of Magenta as Blue's girlfriend.
Periphery Demographic: The show was surprisingly popular even with older kids and parents—possibly due to a combination of Parental Bonus and the fact that Steve's jokes, while simple enough for kids to understand, weren't so painfully lame as to be unfunny to everyone else.
In fact, most college students will outright admit to watching it, or that was at least true when the show was still regularly airing new episodes, and particularly when Steve was still on.
Replacement Scrappy: Lots of people don't like Joe. Why? He isn't Steve. To be fair, though, he does just as good a job as Steve, he's just a little more enthusiastic about it.
It should be known that most who don't like the character of Joe have nothing against his actor, Donovan Patton.
Viewer Gender Confusion: Hoo boy... Most of the confusion stems from the lack of Tertiary Sexual Characteristics on Blue; she lacks eye lashes or a slim build as one might expect. She never speaks, just barks, and the pitch is deep enough that it can't be distinguished as explicitly feminine, unlike most cartoon dogs. Also, she is colored (and named) blue, often thought of as a boy's color by many children and parents alike.
It doesn't help that in one episode, Steve refers to Green Puppy (another girl character, and a friend from Blue's school, but voiced by a male voice actor, Adam Peltzman, show headwriter in later seasons) in pronouns twice: once with a male pronoun, and again with a female one. And this was the only indication of Green Puppy's gender for a while.
Anyone else think Periwinkle was a girl when they were a kid?
Thank goodness for Spanish's gender specific adjectives!