Houseki no Kuni is a pretty underrated CGI anime, at first I didn't want to watch it because of the CGI art style but then I watched it and it ended up being really good. I've seen some YouTubers talking about it but I still think it's underrated.
Well two Anime I could say, is Dream Eater Merry/Yumekui Merry and K Project bother of those Anime are great. While I will admit Yumekui Merry didn't completely follow the manga, it was still a great Anime to it's self and K Project, I personally think it's amazing but that's just my opinion. It has great graphics and a touching story.
Blood-C: A guilty pleasure of mine. Typical sailor moon formula with a bloody and edgy theme. Schoolgirl by day, monster slayer by night. The story picks up halfway through and the ending is just epic. it left me wanting more and seeing a conclusion to the story.
Sadly the movie for Blood-C was just awful, they screwed up the finale we were all waiting for.
Medaka Box Abnormal: Medaka box is one of those really insane meta shows, where I feel like the writers were given complete freedom to just make the most interesting story they could come up with, and the animators would make it beautiful at the same time. It covered a lot of concepts in a short time. to bad they never really got anywhere with the show.
serial experiments lain is pretty fun to watch and i find it to be often forgotten.
mind game. it's a movie, the concept isn't anything new, but it's not talked to death like other more popular ones like, let's say, tenshi no tamago (which is excellent but everyone and their grandmas talk about it).
i don't watch a lot of anime, mostly read the manga and don't bother with the animated adaptations.
good luck finding manga physically on portugal, apart from the usual shonen stuff xD i found monster to be one of the most interesting mangas i've read. the anime is quite boring and gives away too much, though. i also liked the concept of barbara.
Idk if it's underrated or not but I really like Shinzo. c: I watched it on Jetix all the time but it was hard since it came on pretty late. vwv I really liked the concept of the show and it was weird and cool for me. xD