The Messenger is a retro-platformer with an interesting twist. It starts off like a fairly standard action-platformer from back in the day, but soon turns into "an expansive time-traveling adventure" that makes use of both 8-bit and 16-bit graphics and audio. And not just for visual flavor but as an actual mechanic: Players can swap between the two styles mid-level to solve puzzles, for instance.
In late 2018 it got a new Game+ mode with a more challenging difficulty, and earlier this year new levels were added in the free Picnic Panic DLC. And now it's free for the week on the Epic Games Store: Hit the page, click the "get" button, take it from there. You know how it goes.
There's only one free game this week, because The Messenger is rated E10+ by the ESRB. (Access to "Mature" games can be disabled by Epic Store parental controls, so whenever the weekly freebie is M-rated Epic gives away a second, more family-friendly game as well, to ensure that everyone gets a game.) There will be just one free game next week too, the tile-based RTS roguelite Bad North: Jotun Edition, which despite the title is actually quite good.