Arguably one of the best entries in the series, The Elder Scrolls III: Morrowind, is free on Amazon Prime Gaming ahead of a new update for The Elder Scrolls Online that will add new Morrowind-related content to the game.
The version released on Prime Gaming is the entire Game of the Year Edition, and while Morrowind dates back to 2002 and is starting to show its age a little, it's arguably one of the best entries the series has ever seen. Whether you're looking for nostalgia or have never played Morrowind, I strongly recommend picking this one up.
You can also find a huge collection of Morrowind mods on GameFront right here, with everything from new quests to graphical improvements and much more. In particular, I strongly suggest grabbing the Morrowind Visual Pack from modder M.V.P. Creaters, and the Morrowind Enhanced Sounds mod by modder pancreas.
Microsoft confirmed at its Developer Direct that big changes are coming to The Elder Scrolls Online based around Morrowind, with a new series of DLC packs named Shadow Over Morrowind starting on the 13th of March.
Elsewhere on Prime Gaming, the excellent Divine Knockout and roguelike Tunche are also up for grabs, along with some new content for Apex Legends, Warframe and Fall Guys.