The Oppenheimer of "Manhattan" should not be confused with the historical Oppenheimer. They have similarities but the Oppenheimer of "Manhattan," like the rest of the show, is definitely meant to be in some kind of alternate universe from our own. In general he reflects the chillier, angrier side of Oppenheimer's personality — one that did in fact exist, and is often downplayed in his more traditional depiction as a scientific martyr — but he also had more charming, warm sides as well.

Oppenheimer was remarkably good at charming people who he wanted to charm, and that included military people and Washington people (most of the time — he could commit faux pas, and sometimes did). He was not extremely involved in the day to day science of the project, at least not after he became Scientific Director (he did some work for the project prior to this). His real contribution to the project was coordination and serving as a liaison to the scientists, the "good cop" to Groves' "bad cop."

I am fond of the portrayal of Oppenheimer in "Manhattan," both because the actor captures his alien weirdness very well, but also because he is such a strong contrast with, say, the "feel good" Oppenheimer of the film Fat Man and Little Boy. The real-life Oppenheimer could be cutting and nasty, had affairs with Communists who later turned up dead under mysterious circumstances, was a man who would sell out his students and friends if it pleased the Army for him to do so, who strongly urged the first use of the weapon against a city so as to display its destructive power, and many other things that "Manhattan" took pains to depict.

On Oppenheimer's life, the best biography currently is Bird and Sherwin's American Prometheus. On the decisions made about "Manhattan," I have written quite a bit about them on my blog — I was the historical advisor for Season 2 and spent considerable time talking with the screenwriters and showrunners about Season 1's choices as well. (Warning: contains spoilers!)