Pretty much anything made by Masaaki Yuasa tends to be under-appreciated in my opinion, his narratives are often unconventional and his art styles tend to be influenced by western animation more than anything and end up being very surreal. I strongly recommend checking out his entire catalog, most of it at the very least should offer a unique experience that's worth having, his 1st film Mind Game as well as a short film called Happy Machine (Which is a part of an anthology series called Genius Party) are surprisingly available on Netflix in the US.
Satoshi Kon is another director who tends to overshadowed by the likes of Hayao Miyazaki, which is a shame because I consider him the 1st great filmmaker of the 21st century, not just in animation but film as a whole. Kon loved blending dreams and reality, intentionally confusing the viewer regarding what's real/fantasy and often delving into a character's psychology which is the kind of stuff I've always loved. Satoshi Kon, before the time of his death had worked on 4 films and a TV anime, all of which are worth watching, though I do think Tokyo Godfathers is a nice place to start, considering it is a Christmas film and the holidays are right around the corner.
Angel's Egg is a film directed by Mamoru Oshii (Ghost in the Shell, Jin Rou) with character designs by Yoshitaka Amano and if that name sounds familiar, it is the same person who is responsible for the character art for Final Fantasy, so hopefully that's convince some people to watch it. The film may be hard to watch due to it's incredibly slow pacing and little dialogue (About a page's worth throughout the entire film) but if you're willing to sit through it, you should be rewarded with a film chock full of atmosphere, symbolism and experimental visuals.
Wings of Honneamise is a film that seems to take place in either an alternate universe or just a different planet entirely, but it follows a young man named Shiro who is a member of the Royal Space Force which is a space program attempting to launch a human being into outer space and follows it from the design stages to the final countdown alongside Shiro's relationship with an incredibly religious girl named Riquinni and a political scheme to prevent the launch of the spaceship, Honneamise. The film is definitely worth watching not only for its pretty impressive scale but because of how it was such a visual achievement it was for its time.
