The interviewed article doesn't imply that he wasn't a good physicist, it says that his contributions aren't comparable to the kind of geniuses like Einstein or Johnny Von Neumann.

It also explains few of the reasons: lack of focus, timing, different scientific culture.

I'm not exactly understanding why so many people are taking the offense either.

The interviewer asks a very straight forward question multiple times: help the reader how does Oppenheimer ranks in his skills and contributions to other physicists of that era and it does just that.