At this point your safest bet is probably Sonic X Shadow Generations. Classic stages play like "what if we broke the physics of the originals and you just shot around everywhere, but also we thought about that" while modern stages hit a nice dopamine thrill ride. Bosses are universally pretty bad to "I don't even know what I'm doing", but that's corrected in the Shadow portion, which is a nice mechanical complexity upgrade from the Sonic half of the equation and just generally feels pretty good.
Otherwise probably still Mania Plus if you want a more direct expansion on S3&K and CD's mechanics, not much to complain about with Mania at all. Gens is just a better bang for your buck for the "what's Sonic been up to for 30 years?" pitch without needing a lot of prefaces. Or is an easy refund on Steam if you get to the Sonic 3 portion and don't vibe with it.
Mario Vs Cloud 2002: A Video Retrospective - https://youtu.be/1dx4t6H_K9Y
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