Similar style or artist?

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French director René Laloux made three animated science fiction themed features that you might find interesting. FANTASTIC PLANET (La Planète Sauvage) was made in the 1970's. His hand drawn animation style is slightly reminiscent of Sylvain Chomet's but be prepared for a completely different pshychedelic head trip for this one. It was followed by TIME MASTERS (Les Maîtres du temps) which he made in collaboration with acclaimed master BD artist Jean Giraud, better known as Moebius (known in Hollywood as a production designer for films such as THE FIFTH ELEMENT and TRON, also his art influenced BLADE RUNNER). Interesting story and less esoteric/enigmatic than Fantastic Planet but not as successful overall as the first film. His last feature film was LIGHT YEARS (Gandahar). The Weinsteins bought the film's rights for English speaking territories and redubbed it with a cast that included Christopher Plummer, Glenn Close and Penn & Teller with the legendary late author Isaac Asimov as the screenplay supervisor. I believe this one was slightly more successful and better known internationally than Time Masters but Fantastic Planet is the definitive best among the three IMO. I believe all three movies are available in one form or another in various territories/regions but I suggest you check out clips available on YouTube first.

You've probably heard of Oscar winning Japanese animator, Hayao Miyazaki who's best known for his epic fantasy adventures like Princess Mononoke, Spirited Away and Howl's Moving Castle. While his animation style is not much like Chomet's, you might find his more understated gems like KIKI'S DELIVERY SERVICE, PORCO ROSSO and MY NEIGHBOUR TOTORO more to your liking.
Miyazaki's films are more upbeat than Chomet's and usually packed with life-affirming, positive messages but his Studio Ghibli partner/co-founder Isao Takahata's films are decidedly more realistic in tone and style. He was heavily influenced by French Nouvelle Vague (new wave) cinema and Italian neo-realism. It's my understanding that he's considered by many as an even greater master than Miyazaki himself, especially in his native Japan. Again, I cannot honestly say that his animation style is similar to Chomet's but as animation films go, his painstakingly created movies are enriched by meticulous details and are an unmistakable labour of love, and in those terms, they merit comparison with Chomet's work. I highly recommend GRAVE OF THE FIREFLIES, POM POCO and his earlier little masterpiece GAUCHE THE CELLIST.

Speaking strictly of 'artistic styles,' there are loads of artists who create short animated films that are hand-drawn, and some boast similar artistic sensitivities to Chomet's. American animator/artist Bill Plympton actually made more than a few feature-length movies which are all hand-drwan by himslef, I believe. I've only watched a couple so far but I like his style which can be 'naughty' sometimes.
Other than that, there's another intersting Japanese artist named Koji Yamamura whose short film MT HEAD (Atama Yama) was oscar nominated a few years ago. His short film anthology is currently available on dvd only as a US import from Amazon.co.uk so I reckon it's still in print in the US. It's called 'Franz Kafka's A Country Doctor and Other Fantastic Films by Koji Yamamura.'
Here's a link to some of his works on YouTube:
http://www.youtube.com/watch?v=UuM8xHQSUEM