Sherlock learns everything and sees everything as relevant.
Sherlock bluntly points out Watson’s faults when Watson says that they don’t know each other and don’t know if they can live together as roommates
Mr. Lestrade looks normal and not like a rat.
The wedding ring was worn by the dead person
The word “rache” is scratched into the floor and was her daughter’s name and password to her phone. Sherlock says the word “revenge” in the floor is too obvious and lame.
Sherlock has all the same characteristics as the character from the book except for the cheerful one I think. They had him be more of a high functioning sociopath.