Diablo III - Patch 2.2, 2.3 and 2.4. Major content patches which added tons of stuff to the game without costing anything.
Definitely this.
Highs:
Diablo 3's free patches have been incredible. They've added new areas, enemies, rewards, legendaries, sets and game systems, including quality of life improvements, and all for a brilliant price. And they're not done, with new hand-crafted (non-randomized) dungeons coming soon along with a host of other updates. Blizzard should be damn proud with how they turned this game around and brought the love back.
Along that same token,
Warframe's updates over 2015 have been bonkers. They completely remade the player traversal systems from scratch, adding unlimited clambering and bounding up and along all surfaces, and have added in new techniques like Max Payne slow-dives, Titanfall wall latching, and a bullet jump that just propels you into the air whenever you need it to the core moveset. Every tileset and area you might have known backwards and forwards over the past two years has just opened up tremendously, as every surface and nook and cranny is now worth exploring or using for stealth and combat.
That's one change among a great many (seriously, they put out a ton of content), with Update 18 including mo-capped cinematic quests and some actually mindblowing reveals from some actually well kept secrets. They're still fucking nailing it with this game.
Evolution has been doing it right with
DriveClub too, not only keeping to their plan of new cars, new events and new liveries every month that made up the now complete Season One, but they also listened to the community and added new features and tweaks just as regularly. And there are more tracks to come in 2016, but we don't know anything in the way of particulars or if a Season Two is in the cards. I hope so.
In a nutshell, if Games-as-Service is the way things are going, these three games should be taken as examples of how to do it right.
Besides those,
DriveClub Bikes has completely surprised me in how different it feels and flows and plays compared to the cars, and
Wolfenstein: The Old Blood gave me exactly what I was looking for - not more of New Order, but more of what The New Order didn't provide. If you want a heavier emphasis on story and character, play TNO, but if you want more intense mini-sandboxes of ultra-violence designed for replayability, you'll find it in The Old Blood.
Lows:
No
GTA V story DLC, replaced with more multiplayer-only reasons to buy Shark Cards.
And a nitpick or
Arkham Knight. I should have done a little research or read the small print, but I bought the Dark Knight Tumbler skin for the Batmobile only to find out it doesn't work in campaign. That means it totally useless for me.
....
All in all my experience with DLC content this year has been far more positive than negative. And its still nice to know that there's more
Bloodborne and
Witcher campaign stuff out there if an when I ever decide to dip into em.
Of course I'm not counting microtransactions, macrotransactions and other assorted resource and XP boosts and randomized consumables and such vapor as DLC for the purpose of this post. That stuff can fuck right off along with Konami.