The Clone Wars story is exceptional and a great addition to the Star Wars cannon. The first three seasons are definitely more kid-friendly, but the themes and story becomes much more adult the final couple of seasons.
Sadly, that's also when the really excellent extra features disappear from the set as well - which is sad as the features from the early seasons are great.
The voiceover work is top-notch and you forget just a few episodes in that the primary cast are not the real actors from the films, however there are a few pleasant surprises and cameos.
As mentioned above, this series was cancelled and this is (at the time Feb, 2014) the only way to collect the entire set. However, Season 6 has been announced and will eventually be released, but there is no indication if it will be out on its own or if Disney will double-dip and release another complete edition with it added on.
With that caveat in mind, I still highly recommend this set and then just buying Season 6 when it's eventually released, unless you are a completionist.