While there is a burgeoning love triangle here, it rightly isn't the focus of the film. There's a war to be fought, you know. Soaring speeches to be made, horses to be ridden, swashes to be buckled, etc.
As far as "acting" is concerned, there is little heavy lifting required of the actors apart from Charlize Theron and the actors that portrayed the dwarves. And considering this film's approach, it works just fine. Kristen Stewart is convincing in her role as the one chosen to breathe new life into the kingdom. I was originally of the idea that it made no sense to cast Stewart as Snow White opposite Theron, because of course Theron is the more attractive one. But I later realized that was the point. Of course Ravenna is outwardly more beautiful than Snow White. She's supposed to be. Ravenna's beauty is artificial, it sucks the life from all around her. As opposed to Snow White's "dark" beauty that has the inverse effect. In short, I'm totally fine with Kristen Stewart in this movie.
This was a far better film than I expected. It reminded me of the magical feeling I used to have as a kid when I watched 80s fantasy movies such as Willow. The crisp, clear, and sweeping HD cinematography and imaginative special effects certainly helped. On a side note, I grow more and more appreciative of the emergence of High Definition in today's movies. The fantasy film genre hasn't fared well since Return of the King left theaters bock in 2004, but this is a decent revival of the genre. Now, I am NOT saying this film is as good as Willow or ROTK, though it is fine in its own right.