Three things:
1. No word on battery. This has been a huge problem for other (sometimes larger) watches. Does it have to be charged daily?
2. More expensive than the competition ($350 Vs. $250 and $150, for the Galaxy Gear+Moto 360/Pebble+Sony Smartwatch).
3. They release in "early 2015" so miss this Christmas holiday season which MIGHT negatively impact adoption (or not, dunno).
4. iPhone only. I understand their reasoning but this will definitely limit adoption somewhat (not really too surprising however).
The battery question is the biggest ??? hanging over this. A watch that can barely last a day (e.g. Moto 360) is a huge negative to a lot of people, myself included.
That's one area where the Pebble really excelled. With its eInk display, the screen was always "on" and it would run for several days on a single charge. We need a combination LCD/eInk panel to get the best of both.