While the Epic Games Store has been churning out some pretty interesting games so far this is one of the bigger ones they've done. The Witness is a very mysterious and interesting puzzle game that will challenge your mind and just about all of your senses. It's based off of one simple puzzle, but manages to stretch that across an entire island with over 500 unique versions of it.
The Witness has over 6,000 reviews on Steam, and has managed to keep a Very Positive average with them. Here's a bit more of a description of the game if you are curious:
These puzzles will challenge and surprise you.
You don't remember who you are, and you don't remember how you got here, but there's one thing you can do: explore the island in hope of discovering clues, regaining your memory, and somehow finding your way home.
The Witness respects you as an intelligent player and it treats your time as precious. There are over 500 puzzles but no filler; each of the puzzles brings its own new idea into the mix. So, this is a game full of ideas.
This to me is up there with Subnautica as the biggest of the free games that Epic has put in the store. It adds to a very interesting catalog of games that have been added, which you can find a full list of right here. Don't forget to grab Oxenfree, which is the currently available game.