There are two standard “complete” points for a single-player game: beat the final boss and 100% completion. Steam achievements and similar systems usually mark both of those endpoints. There is one achievement for each, along with at least a half-dozen achievements for each aspect of the game you might take to 100%. These collective 100% achievements are what we call meta-achievements: the achievement for gaining achievements, in this case all the other ones. MMOs are fond of having many achievements that build to meta-achievements for each dungeon, special event, etc.
Guild Wars 2 has moved to setting meta-achievements below 100% without a 100% completion achievement. As mentioned, I think that is a great idea, particularly when the achievements are scattered across different types of content. You encourage diverse play without making someone feel “forced” to do everything to get the shiny prize. This is especially true for events and new content, because sometimes the new content does not work as intended or is radically polarizing, and you should not encourage people to play your most painful content. Team Fortress 2 learned this lesson with its class updates, originally going with “complete all the achievements to get the meta-achievements” and tying new equipment to those meta-achievements, which led to radically aberrant gameplay; class meta-achievements are now done with about half the achievements.
I think I still want 100% completion for single-player games. Those are for completionists, not everyone, although I want no one-way doors on that path. For my MMOs, I like having a bar below “do everything” because I hate that night where you make 20 attempts in a row because the event is going away tomorrow (or worse: time-limited, attempt-limited, non-tradable, random drop collection achievements).
The Queen’s Jubilee does this somewhat differently, and I will address it in a separate post.