Syndicate—the Bullfrog one—was a fantastic, groundbreaking game. But it's 22 years old, and as much as I loved it back in the day, I'm not blind to the likelihood that contemporary gamers might find it tough to get into. That makes it hard to recommend, even with major caveats. But now it's free, at least for awhile, and that changes things.
Syndicate is famously bloody, but I think it's sometimes forgotten that it doesn't portray violence in the name of a good cause. You, as a ladder-climbing corporate executive, literally kidnap people off the streets, forcibly convert them into cyborgs, and then use a steady stream of mind-altering drugs to control their behavior as "agents." (Seriously, have a look at the opening cinematic if you don't believe me.) It was wantonly amoral, and even the most murderous excesses carried no real penalty as long as the job got done.
That makes it a game worth trying in my book, and even though the standard $5 price tag on Origin is hardly a big investment, free is even better. It's the usual "On the House" deal, meaning that for as long as the offer lasts, you can sang the whole thing at no cost, and keep it forever (or at least until EA pulls the plug on Origin). For some reason, the download is 27MB, which is noteworthy only because the game originally came on four, or maybe five, 3.5" diskettes, meaning it was, at the absolute most, somewhere shy of 7.5MB.
It runs flawlessly thanks to some pre-configured DOSbox magic (which is probably where that extra 20MB of weight comes from), and it is very dated: The control scheme lacks a number of features we take for granted in modern RTSes, like click-and-drag to select multiple agents. But it's free—and at that price, you can afford to take a chance.