While elders of Kaurava court feel greatly blessed by Krishna's Vishwaroopa darshan, Duryodhana views it as "conjuring trick"!

Krishna's Vishwaroopa in Kaurava court during Krishna's peace mission is viewed as a great blessing by Dhritharashtra, Bheeshma, Drona, Vidura and rishis assembled there, but Duryodhana is not impressed!

While Kamala Subramaniam's description of this Vishwaroopa (in her book, Mahabaharata) runs into a few paragraphs, even wikipedia has a short description of it. Given below is an extract from https://en.wikipedia.org/wiki/Vishvarupa :

When negotiations between Pandavas and Kauravas break down with Krishna as the Pandava messenger, Krishna declares that he is more than human and displays his cosmic form to the Kaurava leader Duryodhana and his assembly. Vishvarupa-Krishna appears with many arms and holds many weapons and attributes traditionally associated with Vishnu like the conch, the Sudarshana chakra, the gada (mace), his bow, his sword Nandaka. The inside of his body is described. Various deities (including Vasus, Rudras, Adityas, Dikapalas), sages and tribes (especially those opposing the Kauravas, including the Pandavas) are seen in his body. This form is described as terrible and only people blessed with divine vision could withstand the sight.

--- end wiki extract ---

I add the key point that just prior to Krishna showing his Vishwaroopa, Duryodhana's plan to bind Krishna up and use Krishna as a hostage to force Pandavas to withdraw from war, is exposed in Kaurava court by Satyaki in presence of Dritharashtra, Krishna, Bheeshma and others but with Duryodhana being absent then. Also Duryodhana is worried that Krishna is advising the Kaurava elders to bind him (Duryodhana) and his key supporters. Perhaps that triggers this mad plan of Duryodhana. Dhritharashtra panics, calls for Duryodhana and after Duryodhana arrives in the court, speaks strong words to him about the madness of such a plan. Krishna then smiles at Duryodhana and says to him, "You poor fool, you think I am alone and that you can capture me. I am sorry for you and your inane thoughts." This is followed by Krishna showing his Vishwaroopa to the gathering in Kaurava court.

...

After Krishna has left for Upaplavya (where the Pandavas are camped), Duryodhana asks a messenger (Uluka son of Shakuni) to convey his messages to Yudhishtira and others, including Krishna, at Upaplavya. Note that this is just before Kurukshetra war starts and these messages are read out openly where Yudhishtira and others are assembled.

In the message to Krishna, Duryodhana who clearly wants the Kurukshetra war to happen with his attitude being that either he should have victory over Pandavas or die in the battlefield, insults Krishna (and his messages to the Pandavas also insults them). In his message, he refers to Krishna's Vishwaroopa shown in Kaurava court as follows: "Krishna, do not think that we were impressed with the conjuring trick which you practised in our court."

"Conjuring trick"! Duryodhana is so full of bad/evil thoughts that he could not appreciate the great divine vision that Krishna gave to those assembled then in the Kaurava court including Duryodhana.

The takeaway for me from this is that even when Avatars come amongst people, few people are destined to be their critics and cannot appreciate the Avatar's divinity even when the Avatar demonstrates his divine powers to them! 

[I thank author Kamala Subramaniam and the publisher of Mahabharata book, and Wikipedia, and have presumed that they will not have any objections to me sharing a few quotes from the above mentioned Mahabharata book, and a small extract from Wikipedia, on this post which is freely viewable by all, and does not have any financial profit motive whatsoever.]