I really like 'A Different Path'. This fanfic takes a unique turn by changing some of the events in the original story. It shows an alternate version of Moriarty's plan and how it affects the other characters. The writing style is engaging, and it keeps you hooked from start to finish.
A good 'Moriarty the Patriot' fanfic should first and foremost stay true to the characters. For example, Moriarty is a complex character with his own motives and beliefs, and any deviation from that without proper explanation can make the fanfic feel off. Also, the plot should be engaging. It could be an alternate take on the story or a deeper exploration of a certain aspect like the relationship between Moriarty and his brothers.
Well, a great Moriarty the Patriot fanfiction could involve Moriarty having to deal with a moral dilemma that wasn't in the original series. For example, he might have to choose between saving an innocent person who could potentially expose his grand scheme or letting them die. Or perhaps a fanfic that shows what would happen if Moriarty's true identity was discovered by his closest allies much earlier. This could lead to a whole new set of power dynamics and character developments.