Sucker Punch is a 2011 Movie directed by Zack Snyder, and starring Emily Browning, Abbie Cornish and Jena Malone (IMDB Page)
Innocents in the line of fire
In the very first scene, we see Babydoll accidentally kill her sister (she was aiming for their stepfather).
In RPGs, we often ignore the possibility of collateral damage, with bullets and fireballs flying around, with no consideration of where they could end up. Bringing this in would make the characters more cautious. As a GM, you might want to mention the collateral damage that the characters are causing, and bring their attention to the innocent villagers that might get caught in the blast when the mage launches her fireball.
Most (possibly all) of the movie takes place in the imagination of one of the characters. This is something that could be interesting in a roleplaying game, with the right group. (With the wrong group, it would just get silly and incoherent.)
To do this, you will need to create several “layers”… Probably in conversation with the players, and have them change layers as things happened.
The action in the movie takes place withing an asylum, which I think could be a unique way to bring the party together. In a game with dimensional horrors that drive people insane, this could be used to bring together characters that have already encountered the mythos.
Running an entire session in an asylum is also an option. It is a perfect setting to induce paranoia and a feeling of isolation, especially as the stuff will not always take what the characters have to say seriously.
During the movie, the main characters are trying to collect the items that they will need for their plan. The thing is, most of the items are fairly common, but in their situation, still hard to get to.
So, in an RPG, it might be interesting to put the characters in a situation where the things that they take for granted are hard to get to.
Rule of Cool
The Rule of Cool states that anything can be forgiven in a work of fiction so long as it is sufficiently cool, which is very obvious in this movie. This is just a reminder to the GMs and the Players out there, that while internal consistency and realism is all well and good, please do not let it get in the way of having an awesome game.
Mecha in WWI
In the World War 1 Sequence, one of the characters is piloting a mecha… Of course, the use of mecha in WWI has left very little evidence, but in my opinion, this falls firmly under the Rule of Cool.
In an RPG, you can play around with that a lot… Perhaps one of the characters in a traditional Medieval setting gets a machine-gun? Or how about ancient greece where everybody has a smartphone?
In all the fantasy sequences, the enemies are not human, allowing the protagonists to slaughter them with no concern. In the case of a typical PC party, the idea of killing other people seem to be not much of a concern, but if you are running a more serious game, it might be fun to throw in guilt-free opponents that can be slaughtered indiscriminately.