Its running Windows CE 6, which is horrible since there will be a total lack of applications for it. I suppose you could say the same about the iPhone, but at least Apple can deliver solid 1st party apps.

Clarification:

There is a difference between Windows Mobile 6, and Windows CE 6. Its an embedded OS and there really isn't anything for it other than what manufacturers install @ launch. I think Meizu's focus is on media playback since thats what they seem to be popular for. Its definitely not an iPhone killer, nor is the iPhone an N800 killer (unless we see some 3rd party apps like Skype pop up).