Based on Mike Pondsmith's seminal Cyberpunk pen-and-paper RPG from the 1980s, Cyberpunk 2077 is set in Night City, a fictional settlement on the coast of California between Los Angeles and San Francisco. The game allows the player to create their own character and determine their name, gender, appearance and cybernetic enhancements. The game is an open-world RPG with a central storyline but also a vast array of side-quests, sub-missions and optional activities that can be undertaken in Night City. It appears the entire city and its surrounding countryside will be available for the player to traverse, either on foot or by vehicle: taxis, Trauma Teams (futuristic amublances), flying cars and a large subway system appear to be available to use, and it seems that the player can also acquire a car of their own (which bears a passing resemblance to Knight Rider's KITT).
We don't know anything about the story, but there appears to traditional cyberpunk goings-on like rich businessmen employing dodgy gangs to do deniable tasks for them, along with significant action set pieces. The game is definitely aimed at mature audiences, with some disturbing cybernetic enhancements and torture scenes shown, along with a spectacular amount of violence.
CDPR's previous game, The Witcher 3, is for my money the single finest CRPG released this century. If Cyberpunk 2077 is even half as good, it will be an essential Day One purchase.
CDPR also released a statement alongside the trailer, confirming that they are committed to the singleplayer CRPG experience, which may be taken as a sly dig at Bethesda's multiplayer focus for Fallout 76 and former RPG titans BioWare abandoning the singleplayer scene altogether in their new game, generic multiplayer shooter Anthem. That said, it's been an open secret that Cyberpunk 2077 will have an online component, but this appears to be a very minor, optional feature (if it's even still in the game).
Cyberpunk 2077 has no official release date, but it appears likely that CDPR are targeting a late 2019 release if possible. Falling back to 2020, the date of the original Cyberpunk pen-and-paper setting, would also be appropriate.