The second levels are pretty similar - push harder than you would normally, pushing "through" your usual action, get haptic feedback, something else happens. One difference that helps discoverability, though, is that 3D touch for stuff like app shortcuts and "live photo" replays has UI-based feedback to tell you there's more if you push harder, whereas the second level push on the MacBook trackpad feels less rewarding to experiment with (or maybe that's just a function of it being used far less in OS X than in iOS).

Yes, there are nuances that most people, myself included, don't understand because we have not used it extensively. This is human interaction with physical objects; there are literally infinite possible nuances.

It doesn't take much effort to look around and see people comparing this to a long press and totally missing the point. I think the pace of Apple's marketing video confused many. So, again, first-hand experience is necessary for me to take any assessment seriously.

3D Touch is completely different to the MacBook's Force Touch.

It's the combination of (a) the effect of pushing through the screen, (b) the haptic feedback when you do so and (c) the way the UI responds to it i.e. by blurring the screen.

Your argument is akin to saying you can appreciate music by reading notes on a piece of paper. Physical nuances can rarely be explained in words.