It's shocking because you can see the visual decline of the series if you watch them in succession. 1-5 are very visually diverse, going for a cinematic approach so that the episodes feel "sepcial". After that, they start to standardize the show's look, and it's more visually bland.

By the later seasons they solidified this completely sterile visually bland look that started in god damn Family Guy and spread to the rest of western animation because of how cheap and fast it is to produce. Everyone just standing around in wide screen flapping their gums. Backgrounds are highly detailed, but you're never going to show them from another angle.