And in the meantime, I think I came up with a query which *does* actually reveal seasonal tendencies. Note that like many others, I listen to anything at any time, so if you looked at a day's listening for me you wouldn't really be able to guess the season, but when averaged over a large amount of data, some patterns seem to emerge.
So for this analysis, I chose four dates (Jan 1., Apr 1., July 1., Oct. 1), and for each album I own, calculated how far away from the target date each listen occurred, and then calculated an "average distance" for the album from that date. For example, on average, I listened to "Norwegian Native Art" only 56 days away (plus or minus) from January 1st, while my listens to "Brave New World" happened 129 days from January 1st, on average. Thus, Einherjer is very "winter" while Iron Maiden is very "non-winter". I filtered the results to only include albums that had gotten 10 listens or more, in a period ranging from one year after their release date to the present (to eliminate false positives where my listens were more dependent on the album's recent release than on the seasons).
There are still some outliers, but a lot of this really fits the gut-feel I had.
WINTER ALBUMS
Einherjer - Norwegian Native Art - 55.8 (Norwegian, sure)
Anathema - Judgement - 57.8 (yup)
Immortal - At The Heart Of Winter - 64.3 (Perfect!)
Enslaved - Isa - 70.7 (What, no 'Frost'?)
Estatic Fear - A Sombre Dance - 73.6 (Sure)
Omnium Gatherum - Spirits And August Light - 74.3 (That chilly Finnish vibe?)
Alchemist - Organasm - 74.5 (nah, this is much more a summer album)
Enslaved - Mardraum: Beyond the Within - 75.1 (what, no 'Vikingligr Veldi'?)
Godspeed You! Black Emperor - Lift Yr. Skinny Fists Like Antennas to Heaven! - 76.9 (sure, I guess)
Root - Kärgeräs - 78.3 (yup, though it rightly ranks higher on the fall list)
SPRING ALBUMS
Dance Hall Crashers - Honey, I'm Homely! - 57.1 (crazy-happy ska, of course!)
Sentenced - Down - 59.3 (yup, 'Down' is my spring-Sentenced, 'Frozen' is for fall)
Blind Guardian - A Twist In The Myth - 61 (yup)
Einherjer - Norwegian Native Art - 61 (still kinda cold in the spring)
Godspeed You! Black Emperor - Lift Yr. Skinny Fists Like Antennas to Heaven! - 61.4 (ok, sure)
Sentenced - The Funeral Album - 63.1 (I guess this is spring-Sentenced too)
The Devin Townsend Band - Accelerated Evolution - 63.7 (oh, totally!)
Ours - Distorted Lullabies - 64.4 (yeah, I can see this)
Primordial - Spirit The Earth Aflame - 64.8 (getting ready for summer)
Without Grief - Deflower - 65.3 (sure)
SUMMER ALBUMS
Iron Maiden - Brave New World - 52.8 (yes, totally)
Angra - Holy Land - 53.7 (yes, totally)
Supared - Supared - 57.8 (yes, totally)
Nick Cave & The Bad Seeds - The Boatman's Call - 60.8 (uh, no)
Primordial - Spirit The Earth Aflame - 64.2 (yes, totally, my 'hot oppressive sun' album)
Peeping Tom - Peeping Tom - 65 (summer party!)
Matisyahu - Live At Stubb's - 65.5 (summer party!)
Demonoid - Riders of the Apocalypse - 65.8 (death metal party!)
Grey Skies Fallen - The Fate Of Angels - 66 (uh, no)
Therion - Vovin - 66.3 (uh, no)
FALL ALBUMS
Estatic Fear - A Sombre Dance - 59.9 (yes, totally!)
Kultur Shock - Kultura-Diktatura - 66.7 (not really)
Godgory - Resurrection - 68.3 (yes, totally!)
Root - Kärgeräs - 68.5 (yes, totally!)
Riverside - Out Of Myself - 70 (yes, totally!)
Meshuggah - Nothing - 72.1 (yeah, sure)
Denali - Denali - 72.8 (yes, totally!)
Devics - If You Forget Me... - 74.6 (yes, totally!)
Forgotten Silence - Bya Bamahe Neem - 75.3 (yes, totally!)
Aterciopelados - La Pipa De La Paz - 75.5 (uh, no)
Growly vocal albums:
Winter: 7
Spring: 3
Summer: 3
Fall: 3
Nordic albums:
Winter: 5
Spring: 4
Summer: 2
Fall: 2
Melodic/classic/power metal albums:
Winter: 0
Spring: 1
Summer: 3
Fall: 0
See, it works!
Neil