one of my favorite games i've ever played is Enderal: Forgotten Stories[0], total conversion mod for Skyrim. liked it way more than Skyrim, includes some new gameplay elements and the story is absolutely phenomenal. while playing it i was constantly in awe of the fact that this was a free conversion made by a low amount of people. played it for about 90 hours over a couple of weeks.
I found Enderal so compelling that I watched a full playthrough, it's the only game I've ever done that with. I wanted to play it all the way through myself, but my PC at the time had very strange audio cracking issues with Skyrim so I wasn't able to get far.
[0]https://en.wikipedia.org/wiki/Enderal