Size and design compared

The Stylus 1 is, in essence, a cross between the XZ-2 and the E-M5 in terms of design. As you can see here it's also midway between the two in terms of size - generally slightly trimmed-down and more petite than the E-M5, but larger than the XZ-2 due to its longer lens and viewfinder housing.

Compared to the Olympus OM-D E-M5

From the front the two cameras look very much alike, with the Stylus 1 being slightly smaller. The main differences on the front panel are the Stylus 1's lens ring mode switch and Fn2 button; it also has a zoom lever on the lens throat.
The design similarities extend to the back of the camera too; both have tilting screens and prominent thumb rests, with buttons clustered on the right side. The big difference is in what these do - the E-M5's offer direct movement of the AF point, which is great for shooting with the camera to your eye, whereas those on the Stylus 1 follow the XZ-2 (and PEN models) in providing direct access to flash and drive modes.
The big different comes from the top down. With its lens retracted, the Stylus 1 is relatively slim; the E-M5 can't match it for portability even when kitted-out with the tiny Panasonic Lumix G 14mm F2.5 ASPH pancake prime. Of course this is a fixed, 28mm equivalent wide-angle; the Stylus goes all the way out to 300mm equiv too.

The top-plate controls are quite similar between the two cameras, but in place of the E-M5's front dial concentric with the shutter button, the Stylus has a zoom lever (and lens control dial).

Compared to Stylus XZ-2 iHS

Here we can start to see more clearly the control similarity between the Stylus 1 and the XZ-2 - both have zoom levers around the shutter button, along with lens control rings and their associated mode switches and Fn2 buttons. The two cameras aren't so different in width either, but the XZ-2 is lower as it doesn't have an EVF. Fit an accessory EVF, though, and it ends up more bulky.
Again, the Stylus 1's control layout echoes the XZ-2's. The latter's fiddly rear dial has been replaced by a vastly better one on the top plate, but pretty well all of the same buttons are present and correct. The record button has moved onto the top plate, with Fn1 taking its place on the camera's shoulder.
The Stylus 1 isn't as slim as the XZ-2 (which itself is no 'shirt pocket' camera), due mainly to the EVF eyecup protruding from the back. Again it has much the same top-plate controls as the XZ-2, but they've all been moved around and an extra dial added. The power button has migrated to a slightly easier-to-hit spot behind the shutter button.