They are, beyond control schemes and visuals, the single best reason to play games on a PC. Mods can, at their laziest, tweak a game so its settings or features behave more to your liking. At their most ambitious, they can transform your entire experience, leaving you with something that feels like an all-new game.
This year was a big one for PC mods, with two - DayZ and Black Mesa - rivalling commercial products for public awareness and, perhaps more importantly, quality.
But they weren't the only great mods released this year, so in the gallery above I'll be highlighting all of the best mods I got my hands on in the past twelve months.
A note on criteria: since we didn't run this category last year, and since the development of mods can be a nebulous thing, I'm being lenient, including not just mods that were definitively released in 2012, but which could also have become prominent or released major milestone upgrades.
Game of Thrones
Paradox' excellent Crusader Kings II becomes, with an exhaustively extensive range of modifications - from the map to the characters to the very political structure of the game - just about the perfect Game of Thrones video game.
It's easy to forget this is a mod at all, so prominent has discussion of zombie survival sim DayZ been this year, and so relatively obscure is the game it's based on, BI's fantastic ArmA II. It's become so successful, in fact, that a proper standalone version of the game is due soon.
Another project where it's easy to forget it's a mod, so extensive are the changes to the source game. Black Mesa was so good, in fact, that we reviewed it as though it was a proper game, probably the highest compliment you can pay a mod.
Battlestar Galactica has been woefully under-sold by its accompanying video games, so it was great to see fans step in where professional studios have failed. Diaspora is a fantastic achievement, bringing the physics and atmosphere of the last decade's most iconic space combat to your desktop PC, free of charge.
Election Total War
Not the most extensive mod for a Total War game, or even the best-made, but this scored big points for how topical it was. And, occasionally, hilarious. Turning legions of Romneys and Obamas into bloodthirsty warriors was one of the year's best commentaries on the partisan brutality of contemporary American politics.
Deus Ex: New Vision
Though it was partially released last year, the final product was only out this year. And what a product it was. The original Deus Ex is a masterpiece, but in 2012 is really starting to show its age, something this "HD makeover" helps alleviate.
Super Skyrim Brothers
Turns Skyrim into the world's biggest, and weirdest, Mario game. That's about all that needs to be said.
Just Cause 2 Multiplayer
Still a work in progress, JC2's multiplayer mod is nevertheless one of the most exciting projects in all of gaming. I mean, they're getting well over 1000 people playing on a single map. That's insane.
Borderlands 2 Split-Screen
Fans do what Gearbox really should have: include a local split-screen option for Borderlands 2, meaning two buddies can get their shoot on in the same room. Makes high fives a lot easier.