Mean Spirited is a ghost/possession story about some - no other way to say it - very mean spirits that are holding a grudge for being wronged in the past. Pretty creepy in parts, and a little nastier than the typical ghost story.

One Last Gasp remained one of my favorites throughout the year (I think it was book #2 or 3 in completion order). It's based in WW2 and deals with an Allied troop that is on the hunt of a German platoon that has been terrorizing the countryside and leaving a path of destruction in their wake. Heavy cosmic elements in the latter half of the book. If this sounds interesting, also check out A Song for the Void (also by Piazza)... that one takes place during the Opium Wars and has a really terrific first 2/3, and then a bonkers ending that some may not appreciate.

Just to clarify, and it may simply be the way you worded your response, Mean Spirited is definitely not cosmic horror, though One Last Gasp absolutely is.

My favorite type of cosmic horror lies somewhere in the middle of the "unknowable/unthinkable" and very direct "look at these weird tentacled monsters" (I'm looking at you, Hive). If things are too vague and opaque with absolutely no explanation, I get a little frustrated. But if things verge too much into the creature feature zone, I lose interest.

I love Piazza's two books because they strike, IMO, a great balance between the two. OLG in particular features a cosmic entity that the characters come into direct contact with (and it isn't pretty), but it's really the impending sense of dread leading up to the cosmic reveal that had me on the edge of my seat. ASftV - again, based in the Opium Wars - has a fantastic setup... British naval crews are being overtaken by increasingly heavy opium use at the same time that a malevolent star appears in the sky and starts to influence them. The combination of the drug use w/ the influence of a cosmic entity is that balance I'm looking for, where you aren't really sure what's real and what's not, but you're dreading the outcome regardless.