It's safe to say that all three of Florence + the Machine's albums have been radically different from each other. The first, Lungs, contains three styles: torch songs, 'big' songs, and girl group pop songs. Weighted, there are more of the first two styles, and to me only 'Dog Days Are Over' and 'Between Two Lungs' fall into the third category, but taken as a whole it feels nicely balanced stylistically.
Their second album, Ceremonials, pointedly favors 'big' songs. This was cool with me because I had loved 'Cosmic Love' and 'Blinding' so much, and now I had even more in 'Seven Devils,' 'Heartlines,' 'No Light, No Light,' 'Spectrum' - wait, actually, the entire second half of the album. Which in hindsight, was not the best choice. (Dudes, it was nominated for Best Pop Album at the Grammy's and lost to Kelly Clarkson. Whom I love, BUT STILL) Ultimately the album felt bogged down in the heaviness, and this was pointed out a lot by fans who were hoping for an album that contained torch songs in the vein of 'Girl With One Eye' from Lungs. They could see what I couldn't because I'd gotten what I wanted. Ha.
Now, with How Big, How Blue, How Beautiful, F+TM have refocused again, this time favoring the girl group pop. If this was a conscious decision, it makes sense - moving away from the mistakes of the previous album but still mining the potential in a style not unprecedented for Flo. It also made it easier, I think, to introduce a much wider range of dynamics and expression with the several moodier, rock-influenced songs on the album. There are no highs higher than anything in their catalogue, but there are much lower lows and it is fantastic.
There is also a noticeable difference in the songwriting. The lyrics finally sound like they come directly from her experiences, instead of consisting mostly of literary enigmas which, while interesting, ultimately can prevent one from fully immersing in a song. 'Various Storms and Saints' is a great example of a track which might be tossed aside as initially uninteresting, except the words and the way she owns them turn it into a performance that gets more urgent and beautiful the longer she sings. Those words are raw, too: "I don't know how I don't just stand outside and scream."