Dieter Bohn at The Verge:
But first, you should know that Project Ara is not, technically, a phone. It’s not even that accurate to call it a project. It’s more like a mission. The end goal for ATAP is to hand off a viable product and stewardship of a hardware ecosystem to Google — Eremenko and his small team aren’t just building a series of proof-of-concept prototypes; they’re attempting to build an industry within an industry.
Project Ara is an incredibly ambitious goal. I like that there’d be way to get a phone with specialised components (like an air pollution sensor, or a hygrometer, stuff like that). I also like that if you smash your screen, you could just pop it out and get another one on the cheap. It would even be cool to be able to add a massive honkin’ battery for long trips or conferences.
Will it work? I’m not sure. I think this kind of diversity of choice in a phone would freak normal people out. Even if manufacturers curate or moderate the choices, I think people will naturally still drift towards the simple choice of a ‘complete’ phone.