If you enjoyed the first half of Death Note, then you
might enjoy Code Geass. Code Geass involves giant mech battles, but the main character is similar in that he's constantly trying to outsmart his enemies.
I'd also recommend:
- Steins;Gate - Sci-fi anime about time travel. Some things seems weird or out of place until the story comes full circle and everything clicks. And I loved that.
- Frieren: Beyond Journey's End - Fantasy anime about an elf mage that didn't really care about forming bonds with people since elves have much longer lifespans (she's over 1,000 years old). But she goes on a new journey and slowly realizes the impact that her previous allies had on her. It's a really touching story with some comedy and action mixed in. It's still ongoing though.
- Eighty Six - A Sci-fi/drama about a group of teenaged soldiers that are forced to fight in a war, by a country that views them as subhuman (because they aren't pure blooded). This show has amazing writing and it made me ugly cry a few times. Just be warned that it can be graphic at times. It does not shy away from the death and destruction that comes with war.