from what i've heard, the styled text/string caused quite a few issues
electric keeps complaining that selecting entities by name now takes way more CPU than it used to.
and the minimessage formatting system has already caused problems when connecting styled texts together, which had to be rectified.
though this may be more of a problem with how features are tested especially with such a complex addition.
the resource pack stuff is nice. took a while to implement it, but it's been executed cleanly. function parameters finally gives everyone ways to compact code further (not requiring a CreateList before a function) as the list of actions keeps increasing.
i'm not sure if the average quality of a plot will increase proportionally to the things that are possible, but time will tell eventually