At long last, Doomfist is free and you can play him on the Overwatch PTR right now.
Doomfist joins the offense roster as Overwatch's latest hero, or villain rather. Blizzard describes the character as a "highly-mobile, powerful frontline fighter." As a character, Doomfist can deal ranged damage with his "Hand Cannon", but also performs slam attacks which knocks enemies into the air. Likewise, you can simply use Doomfist to charge into a crowd with a rocket punch, or break crowds using a move called "Meteor Strike."
Unfortunately, Blizzard also told USgamer that actor Terry Crews will not be voicing Doomfist. The internet—and Crews himself—campaigned for the role as interest for the Brooklyn Nine-Nine actor to voice the offensive character grew. Alas, it was not meant to be this time around.
Doomfist is one of the earliest characters teased by Blizzard. Mentions of the character appear as early as the first cinematic trailer for the game, and recent blog updates by Blizzard as well as cosmetic changes made to the Numbani stage suggested that the character who goes by Doomfist (aka Akande Ogundimu) would be incoming. However, it's very much like Blizzard to just suddenly release the character onto PTR without much notice.
Blizzard also released several supplemental materials about Doomfist's abilities and backstory which you can see in the video above. As you can see in the the amazing, animated video, Doomfist is an out-and-out warrior, who practically murders Tracer (or at least turns her into a time-travel paradox or something).
You can also get a better look at Doomfist in the images provided below. Basically, yes, he does have a big robotic fist that destroys things. You can also see him hanging out with Reaper, Widowmaker, and Sombra, the other members of Talon— so I expect to see fanart and fanfiction of them all hanging out very soon.
Still bummed about the Terry Crews news though.