Aderyn (http://archiveofourown.org/users/aderyn/pseuds/aderyn/works) has been writing two series of 221Bs, Compounds or Stars and Natural Facts, that are gorgeous prose poems. As a group, they cover both seasons. Most explore the bond between John and Sherlock, but many feature most of the other characters. If you love poetic prose and vivid imagery, I would dip into the series wherever you like, as the 221Bs are not arranged chronologically, or feature a narrative arc. A few of my favorites:
"Bright Morning Stars" (http://archiveofourown.org/works/339706), "Break, Burn Blow" (http://archiveofourown.org/works/373045), "B'ville Blues" (http://archiveofourown.org/works/381097), and "Weird" (http://archiveofourown.org/works/369130).