It's good, but the best? I disagree.

December metal releases

05.12 * *Noctiferia - PAX
05.12 * *Cretin - Stranger
05.12 * *Sarpedon - Anomic Nation
05.12 * *Revel In Flesh - Death Kult Legions
05.12 * *Cruachan - Blood For The Blood God
05.12 * *Scanner - The Judgement
05.12 * *Coronatus - Cantus Lucidus
08.12 * *Faithful Darkness - Archgod
08.12 * *Taake - Stridens Hus
08.12 * *Death Wolf - III: Östergötland
08.12 * *Pythia - Shadows Of A Broken Past
09.12 * *Lynch Mob - Sun Red Sun
10.12 * *Krimh - Krimhera
10.12 * *Dir En Grey - Arche
10.12 * *Uli Jon Roth - Scorpions Revisited - Volume 1
12.12 * *Unheilig - Gipfelstürmer
15.12 * *Self-Inflicted Violence - The Sanctimonious Hypocrites Of Reality
15.12 * *Witchbreed - Queen Of Storms
15.12 * *Zero Down - No Limit To The Evil
15.12 * *Hetroertzen - Ain Soph Aur
17.12 * *Demians - Mercury
17.12 * *Angra - Secret Garden
19.12 * *Barathrum - Warmetal
24.12 * *Ascension - The Dead Of The World
25.12 * *The Project Hate MCMXCIX - There Is No Earth I Will Leave Unscorched
31.12 * *Six Brew Bantha - Intravenously Commodified
31.12 * *StarGazer - A Merging To The Boundless
31.12 * *Scarab - Serpents Of The Nile

well this is neat; hadn't heard this was a thing

Yeah, that was my highlight of this month too. Listening as soon as it drops on Rhapsody. Probably gonna check out the new Dir en Grey and Stargazer as well.

Maybe Witchbreed but only heard a song or two that may not be very definitive

This is a new one in the UK, Abandoned State by Shalom Maddar which was released on the 6/12. A french blog lifeisaminestrone-over nominated it a refreshing discovery of the year.

anyone familiar with the artist?

Paloma Faith's new album isn't there.

I don't know if these are mentioned in other comments but they're not on the main list so here :3
Rosanne Cash - The River & the Thread (January 14)
Of Mice and Men - Restoring Force (January 27)
The Gaslight Anthem - The B-Sides (January 28)
Dolly Parton - Blue Smoke (January 31)
Eric Paslay - Eric Paslay (February 4)
Suzy Bogguss - Lucky (February 4)
Frankie Ballard - Sunshine and Whiskey (February 11)
Hurray for the Riff Raff - Small Town Heroes (February 11)
Noah Gundersen - Ledges (February 11)
Robert Ellis - The Lights from the Chemical Plant (February 11)
Phantogram - Voices (February 18)
Dierks Bentley - RISER (February 25)
The Fray - Helios (February 25)
Don Williams - Reflections (March 11)
Tokyo Police Club - Forcefield (March 24)
Johnny Cash - Out Among the Stars (March 25)
Jonny Two Bags - Salvation Town (April 1)
Nickel Creek - A Dotted Line (April 1)
Miranda Lambert - Platinum (April 6)
Needtobreathe - Rivers in the Wasteland (April 15)
Sturgill Simpson - Metamodern Sounds in Country Music (May 13)
Jack White - Lazaretto (June 6)
Rival Sons - Great Western Valkyrie (June 6)
Lana Del Rey - Ultraviolence (June 13)
Willie Nelson - Band of Brothers (June 17)
Old 97's - Most Messed Up (June 27)
Old Crow Medicine Show - Remedy (July 1)
Weird Al Yankovic - Mandatory Fun (July 15)
Anberlin - Lowborn (July 22)
Spoon - They Want My Soul (August 4)
The Gaslight Anthem - Get Hurt (August 19)
Brad Paisley - Moonshine in the Trunk (August 26)
Shovels & Rope - Swimmin' Time (August 26)
Thousand Foot Krutch - Oxygen:Inhale (August 26)
Robert Plant - Lullaby and... The Ceaseless Roar (September 8)
Lee Brice - I Don't Dance (September 9)
Black Veil Brides - IV (October 27)

It was a horrible year for new music :(

Not really. You want some recs? I see you like jazz, check out the releases from Marc Ribot Trio, Peter Van Huffel's Gorilla Mask, Icepick, Paal-Nilssen Love, John Zorn (Valentine's Day, specifically), Marc Ducret, and Ken Vandermark. There was also a fantastic live Coltrane release called Offering: Live at Temple University that I'm sure you'll like.