Yeah a nameplate owned by Activision Blizzard now (the old Vivendi software nameplate was dropped) out of France. Sierra was shutdown by them in '08.
Hands down HQ/QFG 1. Followed by 2,4,3 (never finished 5). Combined so many different types of gameplay into a single game, and still had memorable stories/characters. You'd get so into those games, you actually would play it through again and again as Thief/Fighter/Magic User just to see what was different in the land of Spielburg, Tarna, Mordavia, Silmaria, Shapeir/Raseir.
SQ and KQ games were great, as well. Though outside of the 80's releases with less competition, they didn't live up to 90's Lucasarts or Westwood studio games IMO. I mean, Loom, Legend of Kyrandia, those were great games with excellent presentation. As an comparison, KQ5? Kinda iffy even tho I spent more time in KQ/SQ. I know way too much Sierra lore than I should.
As an aside, as I've grown older, I've started to respect the KQ/SQ series for a lack of violence (but the end-game of SQ1 made it that much more sweet). As much as I enjoyed being able to smash someone in QFG. Something bothers me seeing kids grow up with realistic Americans vs. Chinese, with modern guns in games today.. violence/war is not a good value outside of self defense.. maybe in the context of a united humanity vs a common foe, or zombies, I'd let my kids play them. Gets em nice and as desensitized as possible, implant ideas of divisions in mankind being acceptable, then go and die in Afghanistan I suppose. Or come home, gain a conscience as an older man someday, and go crazy dreaming about what he's done to other living creatures. Maybe committing suicide like so many. Quite an extrapolation, I digress. But I do think I'm onto something, I don't even buy realistic wargames for myself for that reason and I'm pushing 30. I'll do something like L4D, SC or QuakeWars:ET instead. Roberta Williams was wise on that one, and her games taught me vocabulary and how to type.
Interesting fact on Sierra is that right before the Roberta and Ken Williams sold the company off, Ken signed off on the last project he authorized, Half Life. Under the concept that they wouldn't do a FPS game without a story (like id titles). I read he really wondered what would've happened if he wouldn't have sold at that point (imagining his untold millions I'm guessing). Tribes was an amazing FPS by them that was already mentioned.