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.
Character Exaggeration: Kuzco's intelligence, big time. In the movie, he's sheltered and spoiled, but savvy enough to know that Yzma is trying to do his job behind his back and that she has a secret lab, in addition to being manipulative enough to play Pacha for a sap twice. In the series, he's often Book Dumb or a straight-up Idiot Hero.
Seasonal Rot: The 2007-2008 second Season in comparison to the 2006 first season. Season 1 was very straightforward, with a standard 21 episodes that formed an almost equal mix of two-part episodes and episodes with two stories (9 and 12, respectably). Season 2 was 31 episodes long, and all but a handful of them were episodes containing stories—-among the exceptions being the holiday specials and series finale—-suggesting the writers couldn't come up with a story to last 22 minutes.
Seinfeld Is Unfunny: The series reused so many jokes from the movie so many times that they became more annoying than funny.
This is Lampshaded in one episode in which the whole "Roller Coaster Inside The Lab" joke was used so many times that it actually couldn't come up with something witty to say that hadn't been said before.
Another Lampshade Hanging comes when Yzma struggles to think of something new to turn Kuzco into and suggests a llama. Kronk asks, "You're kidding, right?"
Yet another Lampshade Hanging in that episode comes when Yzma tells Kronk to pull the lever, and Kronk does, causing something they've seen before to come down. He then keeps pulling the lever saying "Seen that, seen that" until they flip in.