When it introduced the Galaxy S5, Samsung arguably unveiled its best Super AMOLED display to date, too. It is able to produce up to 500 nits of brightness - something only Nokia has managed to do so far with its OLED screen panels. This peak brightness level places it on equal footing with some of the best LCD displays out there, which are also in the 500+ nits club.
In terms of color representation, the Adapt Display automatic mode on the S5 seems to produce more toned-down hues, compared to the oversaturated colors that the Super AMOLEDs on the Note 3, and Galaxy S4, manage to produce, as you can see in the comparison pics below. In fact, the display test graphics at the end of the slideshow demonstrate that the Movie Mode of the display brings it pretty close to the standard RGB color gamut, with oversaturation in the greens only.
S5 vs Note 3 in direct sunlight
Combine the high-brightness regime, with the traditionally low screen reflectance coating that Samsung applies on its flagships, and the Galaxy S5 might turn out to be one of the best screens in terms of outdoor visibility, though this has yet to be tested. For the maximum brightness to kick in, the light sensor apparently has to be on, and placed under strong illumination, or direct sunlight, just like on Nokia's Lumia flagships. As for color credibility, your best bet will evidently be the Movie display mode, as usual. The other modes produce the typical flashy, far-from-natural colors, that we've come to associate with Samsung's AMOLED panels.