Hehe, there are always things to tweak for sure. An expansion is never truly complete
. Biggest blunder so far in New World is the subpar wording on Mountain Lands. The rulebook also has problems and would benefit from a second pass.
Enterprise (linked by LastFootnote above) is probably one of the longest, most ambitious fan expansion out there. So it gets a big fat thumbs up from me as well.
Of quality as well, I can redirect you toward
Asper's massive set of cards tweaked and tested over the years. Sadly, the pictures have been taken down, but Asper did mock up some cards for each of the entries in the thread. I'd also like to recommend
Dominion: Venus, made by Carline. The quality of the cards (with pictures!) there is phenomenal. Carline has applied the comments and suggestions from the Discord community and as such, the final product has very high standards.
There are more fan expansions out there, but these are the 2 others that immediately popped in my noggin'.