I have a Lumia 640 on W10 running the production build and it works pretty well. There are some bugs: data usage on cellular does not work, Edge sometimes refuses to do anything--just locks up, sometimes Edge crashes sending you back to the home screen, etc. Probably the most annoying thing I find that happens routinely is that when trying to share an image or something from the web via text message it almost always takes two tries for it to work if I want to send a message also. In other words, I will click the share icon, then I click Messaging, and I see the photo attached. If I immediately hit send it goes out fine, but if I try to type a message with the photo it crashes. However, do it a second time and it works every time. Super annoying since I do this multiple times each day! Otherwise I like the Outlook app a lot--handles email from multiple accounts really well. I think the general design is good, though I'm not sure it looks as good as WP8.1. Still looks a lot better than Android or iOS, which are downright ugly! If design is important to you Windows 10 mobile is the best at the moment. Personally, not many apps I miss. I have decided not to do banking on my phone anyway, so don't miss the banking apps. Snapchat is just trash--if you want it, go elsewhere. Twitter is much better than it used to be. The default apps are all quite good.