The Samsung engineers that worked on the Galaxy S7 had a clear path ahead of them. Consumers find the S6 design pretty, so keep it intact for the S7. Consumers think the S6 battery is too small, so bump up the capacity. Consumers want the microSD slot back and few competitors offer waterproofing - so bring both back on board. Finally, add a camera technology nobody else has and the sales pitch is ready to write itself.
The LG G5 engineers decided to think outside of the G4 box. They created two defining, unique features for the G5, the dual camera on the back (which we think will be used often and with great success) and the modular design (which we fear might fizzle out).
The metal casing hides additional secrets, however. Your eyes are first drawn to the 3D Arc Glass, a uniquely shaped Gorilla Glass 4 that slopes at the top, instead towards the bezels. Then there's the seam that runs along the side of the phone.
It's not actually a seam between two pieces of the chassis, it's the antenna lines. Metal phones have (often unsightly) plastic strips that break up the hull to allow antennas to do their work. LG hid those using a technique called "microdizing", which created the "seam." The edge that it creates spoils the exterior slightly and feels sharp to the touch - not enough to be uncomfortable, but it takes some getting used to.
It turns out that the LG G5 is metal on the inside, but it has a thin coating of primer and an additional pigment layer that contains metal particles. The G5 mostly looks the part, but in the hand, it feels somewhere between naked anodized aluminum and polycarbonate. LG claims this is to improve durability (naked aluminum is easy to dent).
The Samsung Galaxy S7 is more traditional - a metal frame with exposed sides is sandwiched between two panes of 2.5D Gorilla Glass 4. The front pane has beveled edges while the back is curved on the left and right, which notably improves handling comfort.
The metal you feel is real (interrupted only by the plastic antenna strips), but most of the surface area is glass. This makes the S7 feel more premium than the G5, but it's also more slippery and more fragile (the glass can crack, metal will not).
The Galaxy S7 is waterproof - IP68 rated, meaning it should survive a dive under 1.5 meters of water for half an hour. No unsightly flaps over ports like we had with the S5 (and it was disastrous if you forget to fit the flap properly in place).
The LG G5 has too big of an opening to waterproof, the whole bottom of the phone comes off! That's the Magic Slot, where custom modules go. LG has two ready at launch - a camera grip (which adds 1,200mAh battery capacity and hardware controls) and a Bang & Olufsen DAC for audio buffs.
It's not as ambitious as Google's Project Ara (where everything is a module you can change), but Ara is far from consumer-ready (if not even dead).
Anyway, the modules are firmly secured in place - there's no wobble at all and no chance to accidentally pull it out. If anything, they can be a bit too hard to remove. Also, since the battery is attached to the module and not the phone, this operation requires a restart (LG worked to improve boot times to reduce the downtime).
The modules don't fit perfectly, though, on our LG G5 unit you can see and feel the module is slightly out of alignment.
In theory, this modular system creates an infinitely expandable and customizable phone. There could be modules ranging from the mundane (a slim battery pack, the camera grip is too bulky for daily use) to wild (an infrared camera).
Could be... so far there are only two official modules (and the B&O DAC will not be available in the US) and no additional modules have been announced.
The Samsung Galaxy S7 is much more traditional in its build. The only thing that comes out of it (and indeed your only opportunity to upgrade the phone) is the card slot, which takes a nanoSIM and a microSD slot. There's a dual-SIM version where the slot is hybrid, it takes either a second nanoSIM or a microSD card.
The LG G5 also comes in dual-SIM flavor, but there the microSD slot is dedicated.
Both manufacturers have elected to disable Marshmallow's "adoptable storage" feature, which merges the inner storage with the microSD. Adoptable storage would have meant the memory card cannot be taken out and read by another device.
Both phones have fingerprint readers and both double as buttons. On the Galaxy S7 it's the Home button while on the LG G5 it's the Power button. Normally your index finger easily reaches the G5's back button, but locking the phone after using the camera can be awkward (as your hand is no longer on the phone's back).
You do get Tap to wake (the S7 doesn't do that), but it's not as fast as Samsung's quick launch solution (double tap the home key).
The Samsung flagship has a biometric sensor near the camera. It tracks your heart rate and your blood oxygen level (SpO2). Those integrate with the S Health app and enhance exercise tracking (in case you don't have a smart watch/band that does that).
LG G5's curious dual-camera setup on the back (which we'll cover in more detail later) comes equipped with laser autofocus and a light color sensor to improve the accuracy of the camera.
We'll get to Galaxy S7's camera too, but for now let's just mention that Samsung made the phone a bit thicker and killed two birds with that particular stone - it fitted a bigger battery and the camera no longer sticks out. The G5 has a definite camera bump.
Before we close this chapter let's mention a couple of tidbits - the LG G5 has an IR blaster on top and FM radio, the S7 has neither of those things. The LG also uses the new USB Type-C connector rather than the plain microUSB 2.0 of the Galaxy. Neither does wired TV out, so practical differences are small (Type-C is reversible, 2.0 cables are much more common).
Innovation: The LG G5 definitely feels like the more innovative product. However, the Magic Slot system will need to prove its worth (and that requires more modules, wider adoption of the modular system and such). The coated metal shell should improve durability, but it spoils the "all metal" feel.
Refinement: The ugly camera bump is gone, our storage needs are free to grow, the phone can weather the elements. The battery is still sealed, but improved battery life is a good consolation prize.
Winner: Samsung Galaxy S7. It's the safe choice - it looks and feels premium and other than worrying about cracking the glass, there are no durability worries here.
We worry that the LG G5's Magic Slot module might get even more out of alignment after a year or two of drops and knocks (and this is regardless of whether you use modules or not). The Arc Glass is cool, but the "hidden" antenna rim often reminds you of its presence and the coated metal feels less premium than it's supposed to.