Costume Quest 2 is the current freebie on the Epic Games Store, offered up as part of their 15 days of free games. You've got until 4pm GMT/8am PT tomorrow to add it to your account, after which it's yours to keep forever.
The Costume Quest series has a simple central conceit: what if Halloween costumes actually transformed you into whatever the costume depicted? The answer is a simplistic RPG in which you explore a world where sugar and costumes are not allowed, with plenty of expected Double Fine charm. Unfortunately Alec struggled with it a bit upon release 8 years ago, due to its combat and systems overly familiar from the first game:
I pushed on past an overwhelming urge to quit, because by its third stage it finally moved on from over-familiar settings and structures to something a whole lot more playful. Its story concerns time travel, Back To The Future: Part 2 is its time travel touchstone, and there's nothing at all wrong with that. I don't want to spoil all the fun, of course, but by coming up with the idea that candy and costumes are outlawed and playing with a 1984-but-with-dentistry theme, it grants more breathing room to a trick or treat concept that had felt tired almost from the moment Costume Quest 2 began.
There's a good chance that if you played the first game that it was 12 years ago, which maybe makes it less likely those systems will be overly familiar to you.
Epic are offering 15 free games as part of their winter sale. They kicked off the freebies with Bloons TD 6, a generous tower defense 'em up that's one of the best rated games on Steam. The discounts in the sale are pretty decent, too, and include 25% off vouchers for all games.