This article, when translated into English, wondered if the show was going to be "empty" since tickets had been on sale for over eight months and still weren't sold out by the time the article was published (on the tenth of July, so two days before the show).
Excuses being given for the poor ticket sales were: that the ticket prices were high (100 euro), that Werchter (Rock Festival) took place only a week before, that there was too much competition since there were free shows going on at the time as well, that Lady Gaga's fans wouldn't want to sit through a jazz show, and that Tony Bennett's fans wouldn't want to sit through a pop show.
So, what ended up happening? Was the show a success?
I don't know if it ended up selling out or not (though I have a guess), but this review gives the show a modest 3/5 stars.
Translated, the article asks, "did we get a good jazz show?"
They answer their own question with a straight "no".
Instead of jazz, they say they were presented with a "musical". They enjoyed Bennett's performance the whole way through, but only liked Gaga some of the time. Complaints were mostly about her belting when she didn't need to be, and about how the jazz bands playing with them, while talented, were basically forced to play a "Disney version" of the songs.
I guess this show was more of the same old thing that we've come to expect from Lady Gaga nowadays: hyped up mediocrity.