Gonna keep it to 1 per composer, otherwise this list would be full of Kajiura Yuki and Kensuke Ushio.
- Garden of Sinners: Kajiura Yuki's magnum opus in my opinion. Great themes, awesome atmospherics. It wouldn't be Garden of Sinners without her music.
- Attack on Titan s1-3 : Sawano's magnum opus imo. The definition of hype soundtracks for me. Never fails to get me fired up during the show. It's a shame that he was replaced for the Final Seasons.
- Liz and the Blue Bird: I dearly love this style of Kensuke Ushio combined with the amazing orchestral piece that the band plays. Kensuke brings such a fragile sound that works really well with the themes of the anime and then the orchestral piece ties the entire thing together. I can't help but cry during the oboe solo.
- NieR Automata ver 1.1a: cheating a bit because I love the game's soundtrack so much and they pretty much straight up used it here.
- Ghost in the Shell (1995): I don't think it needs much explanation.
- Violet Evergarden: Evan Call's use of wind instruments is incredible in this soundtrack. It works so well.
Honorable mentions:
- Monogatari series: soooo many amazing themes
- Chainsaw man Reze Arc soundtrack: Kensuke Ushio again. Mostly because of the pool scene. The rest is really good too though
- A Silent Voice: another Kensuke Ushio one. That one scene... Fuck dude
- Apothecary Diaries
- Terror in Resonance: mainly for the tracks with Arnor Dan
- Madoka Magica: Kajiura Yuki
- Fate series (ufotable run): Heaven's Feel in particular. Incredible work by Kajiura Yuki again. My main issue with Zero and UBW soundtracks is that the theming isn't that strong.
- Fate/Stay Night (Deen version): for all its faults, the soundtrack is actually quite good and is kinda why F/Z and F/UBW have gone down in my ranking for soundtracks due to the themes.
- Frieren: Another good Evan Call one, but Violet edges this one out because it has stronger themes imo.
- Land of the Lustrous: great arrangements. Using different arrangements for different groups isn't necessarily new, but it's executed brilliantly here.
- Clannad: the dango theme never fails to make me cry
- Cowboy Bepop
- Your Name
- Yuru Camp: I love the simple and relaxing guitar soundtrack