I only first watched Clone Wars as an adult, because when I was younger I refused to watch it because I liked the 2d animated Clone Wars cartoon and was upset that the 3d animated show was out of canon with it.

The movie is widely regarded as pretty poor, and there are a fair few bad episodes, especially early on. And it's a deliberate character choice to make Ahsoka annoying at first as part of her character arc.

But the show is really, really good. It highlights a number of things the movies were never able to properly emphasise, like the corruption of the Republic and especially the failing dogmatic strictness of the Jedi order.

Someone produced this guide as to which episodes to watch:

The place I saw it linked from also said the first 4 and last 4 episodes of season 6 (which wasn't out when this guide was produced).

From a quick look at the guide, I'd say most of the "honourable mentions" are also worth a watch.