If you purchased the Assassin's Creed: Odyssey Gold edition, or purchased the game's season pass, you'll get access to a new remaster of Assassin's Creed 3 this March. First released in 2012, the original game is clearly ageing, so it's nice to see it getting some spit and polish.
According to an FAQ on the Ubisoft website, the remaster will boast higher resolution textures, new character models, a new Physically Based Rendering system for lighting, as well as denser crowds, environments and VFX. On top of all that, you'll be able to upscale the game to 4K and HDR.
The information sheet also promises improved gameplay mechanics, with "several features being revamped or tweaked". But it doesn't specify what these changes are, as yet.
The remaster will come with all the usual post-launch content, such as Benedict Arnold Missions, the Hidden Secrets Pack, and all three episodes of the Tyranny of King Washington. You'll also get a copy of the Assassin's Creed: Liberation remaster, which was formerly a PS Vita exclusive. For more details on all that content, this has you covered. It's so far unclear when the remaster will be available as a standalone purchase, but I'd assume after the March 2019 initial release for season pass holders.
Chris Thursten reviewed Assassin's Creed 3 back in 2012, writing that its "entertaining storytelling and fantastic naval combat [is] marred by terrible mission design and endemic feature creep."