I'm on the similar note with trin here - 2013 wasn't the most metal year for me, at least when it comes to new releases. For a good part of the year I had no time to actually listen to music properly, and when I did, I either listened to albums I've missed in the recent years, or some old schoöl trve kvlt stuff of the '80s and such.
Anyway, for 2013, my favorite release isn't metal, but post-punk...
Beastmilk - Climax
Album is available on bandcamp for free listening, do try it out. Great stuff, even though I liked their earlier EP a tad bit more.
Other releases I've liked are already mentioned - Carcass, Caladan Brood, Amo. I'll also add Darkthrone - their latest album is a bit weaker for me, compared to the previous few, but it's still awesome. Ulver of course.
I'm surprised no one added Leprous...or was it previous year's effort?
As for my local scene, I'll put two bands - The Stone, with their compilation Crna Hronika - collection of rare tracks by this Serbian bm band. The first Serbian bm band, if I'm not wrong.
The other one is Nadimač - these guys mix speed/thrash and everything possible for a really killer fast record. I haven't enjoyed their previous releases much, but this one got me.
As for the de facto favorite metal release, it is an EP/demo by a obscure, but amazing band - The Committee! Their first release, Holodomor, is absolutely amazing. They have a full length incoming for 2014, and I'm pretty sure it will just as dark, creepy and amazing as their demo. Not the easiest band to get into, though.
Also, I'll add that I believe that Toxic Holocaust's latest release could've been a winner for me for this year - but I'm ashamed to say that I haven't listened to it fully yet.
In fact, below is the list of all quality artist whose latest releases I've missed...there's time, I hope:
Lustmord
Altar of Plagues
Chelsea Wolfe
SubRosa
VHÖL
Inquisition
Manilla Road
Makes you wonder what the hell have I been listening throughout the year...
And to be an a-hole for a finisher, I already "hate" Alcest's upcoming release. Not really hate, but I've heard that one song, and read a few reviews. It seems that Alcest have lost it, really.
I'll need to listen to the album myself, to make a proper judgement, but it seems to me it will be a downer. Missing metal elements aside (I could live with that), but it seems Neige has totally changed the original concept of Alcest. Disappointing, really.