I will not at all say a lot about the OS itself - because everyone has to get an idea itself, best in test in someone of a Windows Phone has. I think the Metro interface very presentable, the Live Tiles super convenient and the integration of services like Facebook after initial skepticism now also very good.
A few pros and cons to the hardware:
Per
Absolutely top speed - never jerking or waiting!
great display even in the blazing equatorial sun (with sunglasses on) is still readable 1A
Processing for this price range excellent
Integrated free navigation system for you can download all available worldwide maps for free and then use offline - as with all Lumia handsets for me a real selling point when I usually have to pay for each "app-Navi" at least 80 and then only the cards for a particular area get!
Camera for this price range as far as I can judge better than me - even middle of the night really get out of usable images.
Con
Battery life smartphone usual standard - For one day of intensive use, it is sufficient, and if you're frugal and times for 2 days but then it's over.
no LTE (in the price range currently no real minus)
Last but not least the app selection, in my view:
As Iphone users of course I also had concerns about the App-diversity for Windows Phone and can now say is unnecessary!
There is only 1 app that I miss: Call a Bike.
For everything else I have found an adequate replacement or even the "parallel" app of the same developer.