Because it was being simultaneously broadcast as a television series and a web series, technically it makes Clone Wars the first Emmy-winning web series.
Anthony Daniels is the only actor to reprise his role from the movies. Most of the other cast is culled from voice actors for the Star Wars video games from Lucasfilm Games.
General Grievous' voice is significantly different in this, rather than his voice in Star Wars: Episode III - Revenge of the Sith (2005) because his actor in Episode III had not been chosen yet. The ending of the final episode allowed for this as Mace Windu crushed Grevious' lungs leading to a possibly changed voice.
The series spawned a movie, Star Wars: The Clone Wars (2008) and a sequel series of the same name. Instead of being a complete reboot the new series expanded upon the original series as it provides backstory for reoccurring characters, and added new elements to the Star Wars Universe. However, in 2014, Disney updated the Star Wars timeline making the new series official canon. Some have argued this series is considered canon as it takes place directly after Star Wars: Episode II - Attack of the Clones (2002) and ends at the beginning of Star Wars: Episode III - Revenge of the Sith (2005), thus fits in with the Star Wars canon better.
During the third season, most of the story takes place on the planet Nelvaan. This is a nod to Nelvana Studios, the company responsible for Star Wars: Droids (1985), Star Wars: Ewoks (1985), and the animated sequence from The Star Wars Holiday Special (1978). Also, the species of Nelvaan resemble the dog-like characters from Rock & Rule (1983), a movie made by the studio.