Valis is extremely disappointed that you haven't watched any of the Ghost in the Shell franchise. That's not necessarily a reason to watch it (:P), but it's generally considered the class of the SF genre among anime, which seems to be a genre you like. Personally, I find the first movie excellent and Stand Alone Complex solid-but-not-amazing--certainly I'd recommend anything in the franchise to someone who liked Psycho-Pass and Steins;Gate.
For similar reasons, Serial Experiments Lain. Whereas the other shows I've mentioned so far mix concept SF with action, Lain is pure psychological SF. Lots going on beneath the surface, but prepare to be confused for a good while.
Since you're watching One Punch Man, I'll throw in a Hunter x Hunter recommendation; like OPM, it comes at the shounen fighter genre sideways, but takes its subversion a little more seriously than OPM's pure comedic parody. By the same guy who did Yu Yu Hakusho, which did a great job of playing straight most of the tropes HxH subverts.
Still recommend Ping Pong The Animation, it's an excellent show and it's adjacent to genres you watch.
Second Chaqa's Rurouni Kenshin recommendation--by which I mean, watch episodes 1-62 unless that's too many episodes, and *definitely* watch the Trust and Betrayal OVA, which is Kenshin's backstory. The latter third of RK is filler hell, which you can skip. *Do not* watch the Reflections OVA, it is terrible. The animation of the show proper is a little dated, but story/characters are solid and I particularly like how it gives a palpable sense of early Meiji-era Japan. Trust and Betrayal is better-animated and more tightly focused on Kenshin himself.
One more: Darker Than Black is SF with supernatural elements, solid action, distinctive characters.
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