Once again, Blizzard is offering a sample to get players addicted to Overwatch, this time lasting all through next weekend (November 18-21).
You'll have access to all of the maps and characters, as well as several game modes, though it would seem not all of them.
You can unlock rewards and progress as if you own the full game, and if you decide to buy the game during the free period, you'll get to keep all of that progress.
You can go to the official blog post here to learn about the game and how to participate next weekend.