Thank you for the spoiler. I will now stay far, far away from Black Swan. I simply cannot tolerate "it was all a dream/it was all in [the lead character's] mind" type movies. I HATE them.
I think it would be unfair to say it all happened in her mind. She had some hallucinations and mental moments that were generally based upon real stimuli--some were overly paranoid reactions, but she did have valid cause for that. Most of the movie is not in her mind or a dream.
You're right, much of the movie does take place in 'real life', but that's not my issue. It is more that the explanation was something I deem to be utterly prosaic - she was going mad. Sure, we all watch B-movies and everything is about alien invasions and cursed artefacts, but throughout the movie it looked like she was going nuts, and lo and behold, she was. I felt like I was let down, that the plot should have somehow twisted in a way that was something other than how it appeared.
I can see how the movie can be thought of as an depiction of how she transitions from White Swan into Black Swan; in some ways her personal journey of exploration of the darker side of her nature. Seduced by her director, pushed by her mother to be something regardless of the cost, reacting violently against something she is not or does not wish to be. But for me, it all boils down to the end. She cracked and all of the creepy stuff was in her head. Umm... that's all?
I get your point about Sucker Punch, regarding how the action is a series of empowering fantasies that match or embellish what they are doing in 'real life'. But to me, it still seems like a waste; that the protagonists are engaging in a very obvious self-deception to make the most of a bad situation. Maybe we're both wrong about Sucker Punch, and that the title itself is a clue that premise of the movie will be fundamentally different from how it is marketed. Maybe it will actually be satisfying despite what I consider a dodgy plot device. But I don't think Hollywood is that clever.