It's a prime example of "style over substance".
It's actually unfair to compare the two, IMO, as they are VERY different. The Micro Series told one story about the Battle of Muunilinst over the span of two years across three minute segments, and used their final year to mostly focus on the Battle of Courscant. The action is incredible, but we don't really get too much from the characters in terms of growth. However, it seems unfair to criticize the show for lacking character development when it was never supposed to really focus on serialized storytelling. There's a reason the higher ups at LucasFilm refer to it as a "pilot series" instead of the "micro series" like we fans do. It was created to gauge interest in a longer-form show set during the Clone Wars, and when it wrapped, George felt like making a more realized show in-house at LucasFilm was a good idea because of the success the show had. In this case, style over substance actually works in the show's favor. If the action wasn't over-the-top using Genndy Tartakovsky's animation style, it'd be completely forgettable, just because of what the show was tasked with doing at the time.
Star Wars: The Clone Wars is a product of realizing that there was interest in that era, even after the films had ended. It was created with the idea that they now had the potential to develop characters further and create new fan-favorite characters without a quota of "this is in the new movie, so we need to showcase it". Far less restrictive. The finale of Clone Wars Vol. 1 (as it was called on DVD) was originally supposed to feature Durge, but since Episode III was coming out the following year, George told the team at Cartoon Network to make it Grievous instead so they could introduce the character. The Clone Wars also had the benefit of being able to tell its stories in a 22 minute format, and if that wasn't long enough, then several episodes could be used to tell the story, i.e. the battles of Ryloth, Umbara, Ahsoka being framed, etc.
When it comes to people liking the micro series over the canonical series, I can understand why. It's a mix of nostalgia and the art style that make it appealing, and Grievous' introduction remains one of the scariest yet awesome moments in any Star Wars media to date. And until The Clone Wars really got started and timeline issues arose, it seemed like both series were canon, so the awesome robo-ninja-cyborg-Jedi-Killer Grievous was at the same time a wheezing, coughing brute. In the early days of The Clone Wars, fans that were old enough to have seen both shows when they premiered could probably have easily chosen the Micro Series as their preferred show compared to the theatrical release and early Season 1 episodes of the new show. It had a rough-ish start, but got it's groove pretty quickly.
The Clone Wars also invalidated a lot of Expanded Universe stuff, which at the time, was still considered canon by fans even if George didn't. RIP Republic Commando novels, among other things. The Micro Series didn't do any of that, so for die hard EU fans, The Clone Wars will probably forever be a harbinger for the coming of the current Disney Canon.
