Sorry, I strongly disagree. Without any overt spoilers, the ending was an outrage - an illustration of human arrogance. There were many ways it could have ended, but not that.
For me, the story was a little too elaborate for its own good. (The film is based on a novel and may have tried to keep too much of its source.) But it addresses a lot of issues. And the rugged landscapes of the film, which was shot in Tasmania, are just the place for an elusive creature to roam. Besides, Willem Dafoe plays the title character. There's a trailer at https://www.youtube.com/watch?v=KgfB9kebFNI
As for thylacines themselves, they've been discussed here and elsewhere. They're probably extinct, but they haven't really left, since they turn up in film and fiction, and they may be coming back, if de-extinction works.