The three that you listed (Death Note, Code Geass, and NGNL) are really the top 3 mind game anime I've seen and it's one of my favorite genres. I'm not sure if there are any other ones out there on that level.
Log Horizon has a main protagonist that is a genius. He pulls off alot of tricks and gets through many situations with pure strategy and cleverness. The first season is great but the second season not so much.
Gyakkyou Burai Kaiji: Ultimate Survivor meets you're criteria to an extent. The main protagonist is forced to play games against others with basically his life on the line. The games can get pretty clever at points (the first arc revolves around a giant paper rock scissors contest with multiple layers of rules/strategies). The only difference with this show is that the main protagonist isn't a genius and he gets fucked over multiple times. He is able to come up with some clever solutions to get through most ordeals.
I'm going to list two more shows you might enjoy even though they're not exactly what you're looking for.
Hyouka is a mystery slice of life show and I thought it had some very clever mysteries. The main character isn't a school smart genius but when it comes to solving mysteries he is basically Sherlock Holmes. Alot of the mysteries aren't world shattering but I found my mind blown more than once at some of the clever solutions that the main character was able to produce. The show can get slow at times but its definitely worth a watch!
You should watch The World God Only Knows if you're looking for a smart RomCom. The description on MAL can explain it better than I can but the main character is a genius who uses his dating sim game knowledge to get girls in real life to fall in love with him. He lays out plans and can see the ending before it actually happens. Each season gets better and the 3rd season is a 10/10 masterpiece imo.