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What you've seen so far is shonen (kids' anime), plus it's for normie kids. You could go a lot deeper.
If you want to descend only one level into the darkness, try watching the Shinichiro Watanabe trilogy:
- Samurai Champloo
- Space Dandy
- Cowboy Bebop
in that order (ranked by accessibility, not by release date). These are probably the most popular anime series ever outside of shonen.