This is the 15558th most frequent German word.
wahnsinnig
Extremely; insane; crazy.
Here 'wahnsinnig' is used as an intensifier to express a high degree of quality, emphasizing the goodness of the concert.
Das Konzert gestern war wahnsinnig gut!
The concert yesterday was insanely good!
In this context, 'wahnsinnig' describes behaving in a manner lacking rationality or control, indicating a strong emotional reaction.
Er benahm sich wahnsinnig, als er die Nachricht hörte.
He acted insanely when he heard the news.
'Wahnsinnig' here serves as an exclamation to convey overwhelming admiration and amazement toward the view.