Showed the overall bleakness of the period, with an ever increasing spiral into madness that caused so much death and suffering, with the Reign of Terror seeming to be the Nadir, but plenty of nastiness after that as well, though I don't agree that it exceeded the Holocaust in depravity and scope.
And a few points along the way where if the players had done things differently, such as the King, things could have turned out very different.
Nonetheless, I'm unsure if the revolution slowed things down overall, or potentially sped things up, as for the French it certainly gave the people a taste of freedom, and showed people in other countries the idea that they could have the freedom too.
While certainly future revolutions and reactions got quite nasty as well, thanks to the French revolution, I think it is hard to tell if over a period of time (maybe 100 years?) whether where Europe was by the end of that worse than it would have been otherwise. Certainly the people who had to live and die during those times were far worse off, but is there an unfortunately bleak prospect that they had to pay the price for the whole to be better off in the long run?
Else the speed of the more conservative factions to reform, if they had retained power all the way along, may have meant it could have taken a lot longer to reach the levels of freedom the people had.
Certainly the concept of Total War that came out of it was certainly a bad legacy.
Re the guards, while they certainly were just doing a job, and after surrendering did not deserve what happened to them, before that they had fired on the people attacking the prison, killing a number. I don't think the guards were guilty of anything other than defending the prison against attackers, but your summary at the top could suggest no attackers were harmed by defenders.