John Gruber, Daring Fireball:
So Samsung introduced two new flagship phones: the Galaxy S6 and the S6 Edge. The Edge has a display with pronounced curves along the sides. The regular S6 is flat. Why do both of these phones exist? They’re not different sizes. Either the curved edge is a good idea or it’s not. Design is making decisions.
Difficult to argue with that.
Forget the fact that Samsung has created a device that is a return to the days of them shamelessly copying Apple's design queues; the real crime here is going half-in on two designs. If Samsung don't know which one they think is best then how the hell am I supposed to know?
The iPhone 6 and 6 Plus have a real differentiator: screen size. They're meant for different people with different use-cases – much like the Samsung Galaxy S5 and Galaxy Note 4. But these two Galaxy S6 phones? Same size, no significant difference in hardware or software features (read: features, not design). So why do both exist?
For me the Edge is the better looking phone and the curved screen edges have legitimate uses and advantages, it seems weird to say this about a Samsung product but it's true – this thing isn't a gimmick. All that considered, why does the regular S6 model even exist at all?