Should we feel good about life?
Some reasons to be happy comes from Dhammapada 197-200:


  How very happily we live,
  free from hostility
  among those who are hostile.
  Among hostile people,
  free from hostility we dwell.
  
  How very happily we live,
  free from misery
  among those who are miserable.
  Among miserable people,
  free from misery we dwell.
  
  How very happily we live,
  free from busyness (materialism, avarice)
  among those who are busy.
  Among busy (materialistic, avaricious) people,
  free from busyness (materialism, avarice) we dwell.     
  
  How very happily we live,
  we who have nothing.
  We will feed on rapture
  like the Radiant gods.


Rapture (piti) comes from jhana (level achieved in concentration meditation)

The above words come from the perspective of monks who have renounced the worldly life.

But even for lay people, it just goes to show that we can be very happy and grateful for all the good things or situation that we have, the good environment that we're in, and the good deeds that we have done.