Just the fact that the form factor (square screen) already looks dated concerns me.
I think we'll start seeing more square screens, not because Apple did it and it's the way or anything like that, but because outside of displaying a clock, a circular screen isn't terribly useful for what we typically do with a computer.
You can flow text to fit the odd shape, which isn't a huge deal, but for a lot of things it flies in the face of most interface design and you end up treating most of the pixels as though they didn't exist in order to better frame most of the information. Inscribe a square in the circular screen and that's typically what you'll use for a lot of applications.
There are certainly some applications where it doesn't matter all that much such as maps where you can never display all of the information in the space available so who cares what shape you capture the representation in, and others where a circle wins out hands down such as displaying the time, but most of the smart features of a smart watch work better on a rectangular display as that's what developers collectively have a lot of experience working with.
Even the Moto 360 realized that the full circle wasn't worth that much and chopped off a bit of the bottom. That's how little those pixels were worth. They could have lopped off the top and sides as well and what would have really been lost?
Yeah, a square watch does looks a lot less elegant than a circle, but these aren't watches. They're smart watches. While Apple is trying to market them as luxury watches to some degree as well, the most important part is that they add value over a regular watch. I think that the battery limitations and other shortcomings make the whole product category a bit ahead of its time, but if these are going to be the future, or even going to try to be the future, they'll need to be able to be able to provide as much information as possible, which favors a rectangular screen.