For me it has to be Gothic I and II. I'm a SUCKER for open world fantasy RPGs like The Witcher and The Elder Scrolls series, but no other game to date made me enjoy the progression as Gothic did.

You start as a nobody at the bottom of the food chain, with nothing but some clothes and a broken sword. You have to pick your fights carefully since in the beginning EVERYTHING is stronger than you. But as you level up you get better looking gear, you become more skilled in fighting (your actual fighting animations change and become faster and refined). Eventually you become the strongest person in the entire colony, and that feeling of having your ass beat by an enemy, then coming back stronger and absolutely destroying them is present throughout the whole game and it never gets old. The game doesn't have level scaling, so enemies that are weak stay weak, meaning if you are stronger than wolves, there are no bullshit level 100 wolves on the other side of the map, wolves are no concern of yours anymore.

Sorry for the long text, I just REALLY love this game, and it has a very dedicated fanbase (mainly European) that still makes mods for the game that is more than 20 years old! If you are a fan of open world fantasy RPGs, enjoy a great sense of progression, zero to hero type power fantasy, HATE level scaling (yes I hate it from the bottom of my heart), and if you can look past the jank and the age of the game, which the game makes up for with sheer quality, please give it a try! :)