a monumental behind-the-scenes villain;
computer technology that would have been sf earlier in our lifetimes;
hypothetical crossovers, e.g., has the Time Patrol penetrated Swedish Intelligence?
Reopening Vol I, I find a purely formal parallel with some of Poul Anderson's novels: a brief background-establishing Prologue that can be skipped on rereading.
As Anderson's Time Patrol series progressed, its author adopted the practice of dating each new chapter or narrative passage. This is particularly helpful in time travel fiction. Larsson's Prologue is dated "A Friday in November." His Part 1 covers "20.xii-3.1" and his Chapter 1 is dated "20.xii." Thus, the chronological sequence is tightly controlled although we are not told what year(s). But the setting is very up-to-date.
On rereading, we can pause and appreciate details not noticed before or forgotten since, e.g.:
Anderson fans, what is Manse Everard's full name?
Larsson fans, what is Mikael Blomkvist's full name?