To some extent, the ultimate achievement of a TAS is to achieve arbitrary code execution (ACE) on a game, although this has been becoming rarer and rarer in newer consoles. The Nintendo 64 is the current interesting ACE discovery frontier as of 2020.
Post ACE, you then get into more subtle categories which tend to be more geometric clipping through wall glitches, but those can still be fun.
The most beautiful TAS content ever made are:
Video 1. Super Mario 64 '120 Stars' in 1:20:41.52 Console Verified by Soul Umbreon (2012) Source.