The happy ending depends on one's persepctive. Lorraine Hansberry felt the audience as a whole really misunderstood the ending of her play. The Youngers are getting out of the ghetto and moving into a better neighborhood. However, they could be and probably will be firebombed, harassed, and threatened in Clybourne Park. Hansberry was almost killd as a child because someone threw a brick through the window of her family's home in a White neighborhood. Her mother then stood guard with a shotgun. The ending of the play is ambiguous. They are going to own their own home and Walter has grown up a lot, BUT they are going where they aren't wanted and none of them is ignorant of this fact. A lot of progressive White people upon seeing this play--thought 'Yay for them.' A lot of realistic Black people recognized the incredible struggle the Youngers were in for. So, the ending is much like life--uncertain bring the good with the bad.
I would say that the ending is a relatively happy one. Walter has stood up for his family, showing more commitment and veracity than he had previously shown at any other time in the work. At the same time, the family getting out of its condition and moving to the suburbs is a move that is done out of the family's best interests. While there are so many social and personal circumstances that are besieging the Younger family, it becomes redemptive to see them embrace the move together and not show fear about. The taking care of the plant, something that was a challenge throughout the play, will now be facilitated much easier with this in mind. Additionally, I think that the expecting addition to the family also provides hope. Certainly, they will face challenges in Clybourne Park and there is little to believe that these elements will not be present. Yet, the family is aware of that and still is willing to take the risk for it is worth the reward. This becomes the essence of what immigration and movement in America is about, a reason for optimism at the end of the play.