After a while, he switched main characters, having more or less exhausted Bob's potential. The "spin-offs" are relatively interesting, but less so.
Bob (S-tier): The Atrocity Archives, The Jennifer Morgue, The Fuller Memorandum, The Apocalypse Codex, The Rhesus Chart, The Delirium Brief (A-tier)
"Mo" aka Bob's Wife (B-tier): The Annihilation Score
Alex Schwartz (A-tier): The Nightmare Stacks
Mhari Murphy aka Bob's former GF (C-tier): The Labyrinth Index
bunch of random unknowns (F-tier): Dead Lies Dreaming
If you want a good, satisfying series, the first four make a good complete set. Rhesus Chart is still good, but sets up the spinoffs, and even if you get a quick return to Bob later, the rest is basically the Magic Lovecraftian Apocalypse, not the underground magic agency that made the series top-tier. The 10th book looks interesting in the abstract, and I'm pretty sure there's a big payoff coming at the end, but I couldn't find myself to care. After 10 months, it's still at 14% read on my reader, because there is absolutely no pre-existing character in sight yet.