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.
I actually thought if I was REALLY underrated, Chivalry of a Failed Knight, it was actually a good series with a likable cast, an mc you could root for and relationship that just happened than dragged it out. Shame still no offical word on a season 2 yet, only rumours.
I also like with Jormungand is in the same universe as Black Lagoon as those were both great series for being shades of grey morally.