8. Star Wars: The Clone Wars Season 7&8
Although the show later received a seventh season in 2020, the original seasons of Star Wars: The Clone Wars were cancelled after Disney took control of the franchise.
Whilst it was a shame fans never got to see the final two seasons of the series as intended, most of the arcs those seasons would have told were released in one form or another through The Clone Wars Legacy. Under this project, these arcs were either adapted into comic books or novels, or were released in their incomplete form. Dark Disciple, which focused on Asajj Ventress and Quinlan Vos attempting to assassinate Count Dooku, was reworked into a book, and published in 2015. The early animation for Crystal Crisis, which saw Obi-Wan and Anakin teaming up to thwart General Grievous from obtaining a huge Kyber crystal, was released on StarWars.com in 2014.
Luckily, three of the stories initially planned were completed and released on Disney+ for the show's final season. These final arcs, namely The Bad Batch, Ahsoka's Walkabout and The Siege of Mandalore, were nearly identical to what was originally envisaged, and wrapped up the series well. Still, it would have been nice to watch all of the stories Dave Filoni and his team were planning before The Clone Wars was cancelled in 2013.