Gothic 3
Its immediate predecessor is almost singularly responsible for cultivating my contemporary taste in RPGs (solo character, exploration heavy, quasi-feudal, choice-based, factional, gritty but not "dark" and where player input matters but is limited by character stats), thus the prospect of a vast, open-world title was eminently appealing.
I invested months playing it at release, exhausting every possible permutation of outcomes and doing my utmost to break the game, whether by massacring every living being, boundary- and sequence-breaking or just messing with the rewards/potion system to acquire ludicrous stats.
Naturally, I also participated in testing each and every version of the Community Patch.; run through the Content mod, with and without the Questpack.
Gothic 3 is an indelibly flawed gem, one that no amount of patches could ever hope to truly polish and, in so many respects, a relic of its time. Even so, it remains a game I will continue to adore...
For the record: I own a physical copy, purchased at release, in addition to having it in both my Steam and GOG accounts. All told, excluding Deus Ex and Arx Fatalis, it is my most played game of all time.