And here's how they stand up next to each other.
Probably the most stark contrast between the GS6 — both the proper model and the edge version — and the G4 is in the materials. The glass-backed GS6 just feels more futuristic than the plastic back on the G4. Never mind "metallic" finishes or ceramic paint jobs. It's still plastic underneath. And while it looks fine, it feels ... like plastic. (That equation obviously changes once you get the G4's leather back on there.)
And while the front of the GS6 edge has that curve, the phones couldn't look more different from the back as well. The GS6 is flat as flat can be. The G4's curve is as curvy as ever. (And, in fact, the front has a very subtle curve to it this time around as well.)
The real battle (aside from the marketing one, which Samsung has been waging and winning for some time) really will come down to how the internals perform. The G4's Snapdragon 808 versus the GS6's Exynos processor. LG's quantum dot display versus a very good Super AMOLED panel from Samsung. And a camera from LG that promises greater color reproduction than anyone else in the business.
It's a good time to be a smartphone fan, folks.