I'd put Fate Zero followed by Fate Stay/Night Unlimited Blade Works on your list. Same studio as Demon Slayer but older and not as nice looking, though UBW's nickname of Unlimited Budget Works is well deserved. Zero was an anime prequel to Stay/Night and actually has adult characters, which is always a nice change. If you like those, the 3 Heaven's Feel movie are a good follow up, as they're an alternate route from the game Stay/Night comes from.
I dropped Slime after the first season. It started out good, but it became tedious, the MC overpowered and I lost interest.
86 is excellent military scifi, well animated with a great soundtrack. Also depressing as fuck.
If You want to try getting in to Gundam, the original series is old and the animation doesn't hold up at all, but the story is still good. There is a 3 movie compilation of the original show, but Crunchyroll doesn't have it. Otherwise, try The Origin, which was a 6 OVA series that god redone as a 13 episode series called Advent of the Red Comet. Crunchyroll has both versions. It's a prequel to the original series that goes through the origin of the main antagonist of the original show. For main timeline (Universal Century) Gundam shows, Gundam Unicorn is also a good entry point. If you want to try an alternate universe Gundam, Iron Blooded Orphans is an excellent standalone series.