Stephen Orth, a fellow long-time Pebble user:
However, to get back, you must tap the tiny on-screen navigation button in the upper left corner (much like the standard navigation controls in iOS). This seems weird to me. I find myself wanting an actual physical button on the upper-left side of the watch that takes me back (much like the Pebble, or even one of my beloved Casios.)
What I think could have really worked is if Apple had placed the “friend” or Side Button on the upper left side of the watch instead of below the Digital Crown — the functionality could be the same — if you’re viewing a watch face and you press the friend button, it works exactly as it does today.
However, if you’re deep in an email, or an iMessage, or a Yelp review, you merely hit the friend button a couple of times to get back to the app screen and maybe once again to the watch face.
I can relate to what Stephen is saying. I like how the Pebble is currently laid out with the buttons.
John Gruber had a good rebuttal on it below:
A hardware Back button at the top left is an interesting idea, but, I think, a bad one. I do agree about the problem though: those tiny on-screen back buttons are too small to tap reliably. I’ve found that swiping from the left edge is a far better way to go back on Apple Watch — so much so that I never actually try to tap those back buttons any more.
For one thing, putting a button directly across from the digital crown would lead to the same problem some people have with the iPhones 6: when they try to press the power or volume up buttons, they accidentally press the wrong one, because they’re right across from each other, and the natural way they hold the phone is with a finger on one of the buttons and their thumb on the other.
I can also relate to John's comment about the iPhone 6 and the power button switch, as can many others, that was a move that took a little getting used to.