How can Notes from the Underground be considered an existentialist novel?

I think that Dostoevsky's work is considered an
existentialist work because it openly declares that there is little in way of
transcendent totality in human  consciousness.  Dostoevsky's "underground man" is the
existentialist protagonist.  He exists, without any sort of sanctuary and refuge from
the pain and agony that exists consciousness.  His predicament and the manner in which
he is depicted fulfills many of the conditions of existentialism.  The lack of faith in
God or religious exploration is one such way in which the protagonist, the "angry man,"
is an existentialist character.  Little in him represents the idea that there is an
external and transcendent end capable of achievement in consciousness.  There is freedom
in the life of the angry man, another tenet of existentialism.  The freedom to live
one's life and actually live in a state of perpetual hurt and resentment is another
condition present in the novel that is akin to existentialist ideas.  This helps to
bring to light the idea that there is a search for meaning and identity which is a part
of the existentialist ideas as well as the angry man's condition in the world, one in
which there is little in way of solidity, and one where there is constant flux and
change.