from my own experience I would say Samurai Champloo and FMA:Brotherhood (if you like classical style music)
Cowboy Beebop seems to be well liked but it was way too heavy on the saxaphone for me. got old REAL quick.
And surprisingly I ended up liking Berserks soundtrack even though its weird as fuck.
OnePunchMan goes without saying.
You have shit taste , One Punch Man is the new Sword art online.
Best soundtracks would be, both for listening value, and in addition the value for viewing experience.
Bakemonogatari - exceptional
Kill La Kill - exceptional
>I know how we all feel about the plot and characters
No, you don't. Especially not with a show as divisive as Geass.
>one of the top 50 of the past two decades
OP asks for the best and you decide to offer up a random one from the top 50 of the last two decades?
Anything Hiroyuki Sawano touches is amazing including but not limited too:
Nanatsu no Taizai
Kill la Kill
Attack on Titan
Also worth mentioning:
All the Monogatari's are good but Neko(white) and OniMonogatari are best. Just listen to this:
Haikyuu S1/2/3 are all amazing for the gym and Shougeki soundtrack is surprisingly good for cooking.
Welcome to the NHK's soundtrack was really nice.
Natsume and PPZ have underrated, or it feels like less known soundtracks.