"Cat on a hot tin roof" counts with the presence of Paul Newman and Elizabeth Taylor in the main roles, what certainly improves the quality of the movie a lot.
Even with the great acting, the movie, however, is not that interesting. It keeps your attention until certain time. After that, everything looks like the same thing repeated over and over again.
In my perception, the movie is about a father that is dying. The "big father" gave all possible material things he could to his family, but didn't manage to give them the most important one: love. That's the main subject. After that, you have a lot of complications, like the bad relationship between Brick and his wife, the difficulties Maggie has to become pregnant, the greed of Brick's family to get his father's heritage and the mysterious case of Brick's dead friend, what still torments him. With all this problems, it's not a surprise that Brick became an alcoholic.
It's hard to say if the ending is happy or not. It's probably neither of them. It meant a change of perspective from Brick, what might push his life towards happier waters. Or not. That's not really clear.
The merits of the production are in the sense of reality that the movie brings. In some aspects, everyone will feel that something in the film can be applied to his own life. It doesn't avoid the fact that the movie abuses of the same formula, however. I would say that the best parts of the movie are the strange beginning and the realistic ending. The movie might not be perfect but it's still worth to watch it. In the end, it's a really good story.