Small issue: The name Euros is in the masculine form (at least, this is what my latin/small greek/grammar studies tell me). I would think Sherlock's family would change it to the feminine ending- for example, masculine ending Hermes; feminine ending Hermia. Thusly, I would think, that even though Euros is the god of the east wind, that they would change it to Eura or Europa.
I am nit picking, but nevertheless, I expect more from the Holms' family, and the EP & showrunners, given their brilliance. (My classics professors would stand up and cheer for me if they were here).
Back to the episode: I wonder how much of Sherlock's addiction was to rescue John, and how much of it was his own relapse due to Mary's death/John's furious rejection. And what is up with Mycroft getting asked out on a date, if this is connected to the mystery or not.