* BrokenBase: Spenser's fanbase skews older, so there isn't a great deal of discussion of it online. That said, Susan is a reasonably controversial character, owing mostly to Spenser's near-constant adulation of her in the narration. If you look at negative reviews of the older books on sites like Amazon, they'll invariably mention Susan in a negative light.
* EnsembleDarkhorse: The tv series made Hawk into one. It even led to his own short-lived spin-off.
* FanonDiscontinuity: It is a common opinion that after a certain point, Parker went on creative autopilot and the books began to suffer for it. Where that point is, on the other hand, is a subject of some debate. ''Rough Weather'' and ''The Professional'', the last two novels published before Parker's death, are widely considered to be the series's nadir, but some fans will place the point of no return - the point where a fan would perhaps do better to pretend that the books ended before then - as early as ''Chance''.
* GeniusBonus: Any given one of Parker's books is a mixed bag of references to film, poetry, history, and theater, to the point where the old Spenser fansite "Bullets and Beer" took a lot of time and effort sorting through it all.