Imagine a weather app that shows today's temperature vs. yesterday's temperature, hour by hour.
To me, yesterday's weather seems like the most logical thing to compare today's to, but if you don't remember yesterday, no weather app lets you go back a day.
(You could look it up in a web browser, but that defeats the purpose of the weather app.)
I came across a similar "new take" on weather prediction in Dark Sky, an app that basically predicts rainfall minute by minute.
What's better than a great feature in a new app? A great feature with an awesome user interface.
It's simple, cool and intuitive. It has nice little functional animations, and there are fun interactions in random situations.