I think there seems to be some misunderstanding about cel animation here. CGI has not replaced cel animation, cel animation is a technique and CGI is a tool. Modern anime artists use a digital cel animation process. It's essentially identical to cel animation, except we use computers to generate keyframes which are then mildly adjusted or redrawn every frame, instead of using 100+ pieces of celluloid sheets.
CGI is generally a garbage way of animating, because it is cheaper to do than have artists hand draw everything on a tablet or computer, so low budget studios think they can get away with cost saving. CGI is a very powerful tool when used correctly, though. For instance, look at Demon Slayer: It is regarded as one of the most beautifully animated anime to date, primarily because of the action scenes involving the breath techniques. Fun fact: Those are CGI scenes. They use a technique where they generate CGI forms and animate them with digital cel techniques to create the fluidity CGI provides with the beautiful, immersive look of 2D animation. The thing is, when CGI is done well, you don't notice.
What I think we lack is the dedication and effort that artists of the hand cel animated generation had.
But anyways, enough of my ranting.
Cowboy Beebop, Outlaw Star, Slayers, Yu Yu Hakusho, Dirty Pair, Wicked City, Magical Princess Minky Momo, Ranma 1/2, Battle Angel, Ghost in the Shell, .Hack// (I know, 2002, but comeone, it might as well have been a 90's anime), Escaflowne, Saint Seiya: Knights of the Zodiac... My list goes on and on and on. 80's and 90's was, thematically, probably my favorite period of anime. Even the ones that were not so good, there's something precious about their aesthetic. I'm not really sure how to describe it.
The most obscure? I'm not really sure. I never really hear people talk about Dirty Pair unless its on some niche forum, but I don't know if its actually obscure or not. I feel like Magical Princess Minky Momo is pretty obscure too, but I'm not sure if I'm just conflating its lack of existing physical copies as obscure.