I did prefer the design of Dark Sky, since the data was larger and more visually separate from the background, allowing it to be more readable at a glance. But I found that after the big update they had essentially the same functionality and the same UI.
It might be functionally the same e.g. It only shows conditions for the next 5 hours - not all day - how can you tell if you need a raincopat if you go ot. I am on an iPhone in portrait mode. DarkSky showed this as a column of data Weather as a row. This is fundamental to the whole UI.
If you compare the # of clicks it takes and the amount of time it takes to interpret information for the same task for Dark Sky vs the Apple Weather app, it becomes clear that the Apple Weather app "isn't quite there yet". But I hope it will be soon!
If your needs are straightforward, then the Weather app is a pretty good replacement.