This is getting really interesting. Between this, the Nexus 5 and the various Lumia's a $649 iPhone is starting to look very, very expensive. Smartphones at the moment seem to have got 'good enough'.
I've just bought a Lumia 520 as a play phone / replacement while I send my HTC One back to be repaired (due to it continually rebooting / crashing - I'm otherwise generally very happy with it).
I had an iPhone 3GS and 4S as well before the HTC One, so I've tried the three main platforms.
Windows Phone is actually very nice for the basics of webbrowsing, sending texts, calling, etc. It has its faults (limited app selection, screen's not amazing, the font hinting is a bit poor), but I'm very impressed with it (and I'm a Linux dev by trade who hasn't touched Windows for many years).