Because I have given some coverage to the predictions of gloom, doom and redemption of the eccentric Rabbi Nir Ben-Artzi, I feel obligated to mention Chief Rabbi Shlomo Amar's comments on the phenomenon as well.

Kikar has the audio interview of Radi Kol Chai and Rav Amar discussing the issue, you can hear it there. To summarize what was said, they discussed the issue without relating to any specific person, just the concept in general of someone making such predictions and claiming to receive messages from god.

Rav Amar said that such people are false prophets in every sense of the word.. and many of them are themselves very distant from Torah and have no yirat shamayim... there have always been false prophets, even in the days of the neviim, and they were cheats who presented themselves as prophets.. there are some in our days who claim to know more than the greatest neviim, yet the lions portion of them falls in the most serious of sins. It begins with stealing money from people, and leads to failings of very serious temptations and temptation of honor. Every person who is concerned for himself should keep his distance form these people. He has no kedusha, no tahara, and it is the use of deception...
There is no such thing as having special powers, and if a person says he can walk to the moon, it is impossible and you don't need to go check it.
Regarding the predictions of Rav Nir Ben-Artzi specifically, Rav Amar said that anyone who checks will see that the various predictions were only said after the events happened.

Rav Nir Ben-Artzi responded by saying that he is not looking to fight with anybody, and he is not doing any bad to anybody. All he wants to do is to help the people of Israel. I am in favor of unity of all of Israel and I have nothing bad against anybody. "I was given a gift from heaven only to use for good things. B"H I have zchut avot that comes from the chain of my ancestors".