Nokia launched this phone as a follow up in their Windows Phone 8 series after the 920 & 820. This was launched along with the Lumia 520. The single biggest improvement Nokia worked on was the weight with the 920 & 820 being significantly heavier. The matte finish is also great to avoid any finger prints.
Things I like:
Gorilla glass 2 unlike the 820.
Slim & light.
Availability of expandable memory.
Clear black display for sunlight readability.
Super-sensitive touch is awesome.
The OS runs really smooth on the phone and not too resource hungry.
Nokia apps like Drive, Nokia Music, Glance, SMS & call filter, #2InstaWithLove, Nokia smart cam, city lens, cinemagraph are amazing.
I use Nokia Drive everyday and offline maps & traffic heatmaps are awesome. If you buy the original Nokia silicone cover the phone looks even more stunning and you can change colors.
Things that could have been better:
Removable battery.
More internal memory to install apps.
External memory only useful for adding media.