The build quality from Nokia is as good as it was in their market leading days, good solid feel and a smooth comfortable in the hand finish. The only possible weak spot maybe the lock screen / power button of the right hand side. It is used a lot to wake the screen up as well as put it to sleep. I expect it will be okay, however Nokia have included an alternative method of opening the lock screen, with a double tap on screen, should it fail. The only removable part of the case is the nano sim drawer, the battery is not removable. This make sense as the case is much more robust without a battery door and has less places to harbour dirt. The new cordless charging system is a real bonus, just place your phone on the charging plate at night and in the morning a fully charged phone is at your disposal. I have only used about 60 % charge for a days usage and still have to go into battery saver territory, not bad.
What about the operating system? The windows phone mobile 8.1 is very good, and leaps and bounds ahead of the versions of a couple of years ago. I tried a windows phone about two and half years ago and had to send it back. I could not adjust the size of text in the contacts fields or in the text messaging, it was so small I could not read it. Vibrate was added to the back button but it could not be disabled. All of this I am pleased to say has been resolved.
I have always resisted going to Apple, and now Microsoft have given me a good reason not to. I love the tile design, it is now even more customisable, so your home screen can be changed on a whim. With the addition of live tiles it really comes alive. The best feature of all is the response of the unit to commands, screen refresh is impressive and smooth flowing. The connectivity with other systems is good. When I started the phone up and added one or two email accounts and calendars within 30 minutes I had synchronised with my contacts, calendars from my Ipad and now redundant Blackberry Bold.
In summary I think Microsoft / Nokia are well on the way to a phone that will get significant amounts of market share back from Apple and Samsung, especially in the business community. This will increase as more of the popular apps are made available.