They say that you'll either hate or love The Mistress. Fortunately, I'm on the love side, and I'm still trying to figure out how some people ended up not liking it. I don't think it's perfect, and I can cite a couple of flaws, but overall, I think it's a pretty good movie.
Sari (Bea Alonzo) is a mistress, a female master cutter. But she's also a mistress in another sense, the other woman of Rico Torres (Ronaldo Valdez). Despite knowing all this, JD (John Lloyd Cruz) still chases after Sari, wanting her even though he knows that she's already somebody else's. It's a common other woman story, with a few twists here and there. But though the story may be pretty common, they manages to make it interesting.
I think most of it is because of the pretty tight writing. The conflict is established quickly. Secrets are out not even halfway into the film and the audience pretty much already know what's going to happen next. But the engaging exchange of dialogue and the performance of the cast keep you watching. You just want to see how it will unfold, how they'll get out the mess. Or if they'd even ever get out.
I've been told that there's something wrong with the execution of the story. But having no background in film, I can't really see what's wrong with it. Sure, there are some problem with continuity such as how the blocking of actors would seem to change, but it's something I can let pass. Two hours passed by pretty quickly and I feel as if every scene either helps explore the complexity of a character or pushes the story forward. There are no unnecessary characters that take too much screen time, and no side stories that doesn't relate to the main conflict. Each primary character is explored, given enough screen time.