I replaced my iPhone 5 (being on iPhone for 6 years) by the Lumia 830 and I am very happy with it. Screen size, brightness and details are very good, better than the iPhone 5. I also prefer the phone design too. You can put an SD card in to increase storage. Also, battery life is much much better being able to last an easy 2 days when I was not even getting 1 full day with the iPhone 5. Camera on the 830 is much better too.
The OS itself is excellent, very stable. His Achilles heel is Internet Explorer being far to be as good as Safari. As far as apps and the store, your mileage may vary depending if you are an heavy apps user or not. I only miss 1 app but I am not an heavy apps user. The phone comes loaded with a good selection of apps (MSN apps suite, Office, Here Drive GPS, Here maps, etc). All in all, it is very good.
Oh and BTW, the 830 is wireless charging ready. Only have to buy a Qi charging plate and you can charge wirelessly. It is on Macrumors front page that wireless charging will be hot in 2015 and Apple will probably try to make people believe they invented it with iPhone 6S or 7 ��