Forget all the mainstream crap that even the normies will rave about like it's the second coming. I want to know about the most obscure titles I've probably never heard of or are so old people don't even realise they exist but are actually all really good.
Three picks of mine that might have not made their way on peoples' radars.
https://www.anime-planet.com/anime/heavy-object
https://www.anime-planet.com/anime/jormungand
https://www.anime-planet.com/anime/tytania
I love serious sci-fi a lot or stuff that borders on it, bonus points if it's got good animation with proper battles, these three anime fit the bill for me. Jormungand is more of a military style anime but I often find these anime that fly under the radar often tend to be the better quality ones rather than the more heavily advertised mainstream titles and isekai trash.
Ten times the overdone edginess of death note but with an actually interesting and pseudo-realistic plotline - instead of going after inmates, this mass murderer goes after the corrupt government and all the evil shit the elites do. Also why it will never get an anime.
If you're on this site you'll probably enjoy it. Don't read the later work by that artist though it's terrible.