The line from Hamlet that best describes that Hamlet is not happy is the one where he regrets not being able to suicide because it is a sin:
"Oh, that this too, too sullied flesh would melt,
Thaw, and resolve itself into a dew,
Or that the Everlasting had not fixed
His canon 'gainst self-slaughter! O God, God!
How weary, stale, flat, and unprofitable
Seem to me all the uses of this world!"
He is so depressed that he wants to commit suicide for this world is so horrible for him, that finds it weary, stale, flat and unprofitable.