One of the things that makes One Piece one of the most original mangas today is the combination of its wacky art-style with its serious and character-development storyline. Most action mangas simply have more realistically drawn characters. Even characters that are mostly used and drawn as comic relief have their serious character-development times. A lot of times, Usopp is used as the joke monkey of the series but has had his important dramatic times such as when
Spoiler (highlight to view)
he fought with Luffy and left the Strawhats for a while
. There's also all the caricature-based characters that are important to the series such as Ivankov (Tim Burton in Rocky Horror), Enel (Eminem), etc. It really makes the series more fun and exciting. Some people may be turned off by the art of the manga but for me its really one of the things that makes it original and great.
Kingdom Hearts managed to turn classic wholesome cartoon characters like Donald Duck and Mickey Mouse into badasses and work well with the Final Fantasy Characters. Forget Sora and RIku. I'd like the main focus to be on Donald, Mickey, and Goofy. Hopefully, they at least get more character development in the next game.
Another non-anime/manga example would be Kung Fu Panda. Its a wacky anthropomorphic martial arts comedy. It does have its serious moments and some character development and conflict. I've actually read some good fanfiction where not only does it keep the whackiness of the movie but also made some more serious storylines that I would wish the writers of the sequel have read.
If anyone could recommend a manga or anime that does the whole whacky/cartoony series with a serious character-development driven storylines well, that would be cool?