-DOS is not the highest-rated (userscore) of all time on metacritic. Only the highest-rated new release (games released in last 90 days). It's still pretty high up there on the all-time list, but it's closer to being in the top 30 or 40.
If you exclude games that don't have many raters (ie less than 50 or so), D:OS has the highest user-rating of any PC game in the last 5-6 years. But yes, not all-time.