It's unfortunate. I recall seeing "A Perfect Murder" and "The Pledge", two movies that were great all throughout that were ruined by a horrible ending. This movie has to be in that same category. The ending was so stupid that it totally ruined for me what was a good romantic movie.
While I agree that the ending was rushed, a "they lived happily ever after" ending would have been cliche and expected. Frankly, I wouldn't have minded a "happier" ending myself, but ultimately, I think the film works better and leaves more of an impact with an unhappy one.
Tennessee Williams didn't like or believe in happy endings for his protagonists because tragic figures living broken lives don't have happy endings. To his thinking, happy endings were for fairy tales and didn't reflect real life. Most of his characters were based on people in his own life, including himself, and none of them had a happy story, so why should their ending be happy? Happily-ever-afters are boring, bland, and predictable -- no drama or struggle there -- and tragedy is always remembered more than happiness. Realizing this is one of the reasons why Williams was so good at what he did. Pollack shared this viewpoint, at least where this film's ending was concerned, and I'd have to agree with him. An unhappy ending was more effective and memorable.
What I didn't like is how alone Willie was left and at such a young age. What became of her and how did she survive? I'd like to believe that Owen finds and looks out for her, but Williams wouldn't have liked that scenario, either. Again, too tidy and feel good-ish.
It would be naive to expect This Property Is Condemned to have a happy ending, considering the opening scenes and the horrid situation characters were living through. The tragedy of Alva coming to a realisation that Hazel whores her out for influential men, then briefly escaping this reality before coming back to haunt her. This Property Is Condemned is ultimately a tragic story, not a romantic one.
I'd rather be hated for who I am, than loved for who I am not.