Apple has used the same Retina display as found in the iPhone 5 and iPhone 5C, in the new flagship model. It's a four-inch screen, and comes with a resolution of 1136 x 640, making it still-sharp at 326DPI.
It's difficult to recommend the display compared to the rest of the smartphone world, as there are definitely better screens out there. The iPhone 6 and the iPhone 6 Plus offer higher resolutions, and larger displays, and the Plus boasts a higher PPI. Whether this is enough for you with the competition being so far ahead is something I'll leave you to work out.
The four-inch size of the screen is good enough though, as while I might be a fan of the larger screen for movies and internet browsing on the Samsung Galaxy S5 or HTC One M8, the iPhone 5S is a good phone for people that hate the idea of being forced to live with a bigger screen they don't want.
It's not perfect though, as despite what Apple would have you believe, the screen is just a tad too large to operate easily with one hand.
With a small amount of shifting you can get the thumb all the way across, but given you have to jiggle the phone in the palm a little bit to do so, it kind of feels redundant.
In terms of the clarity of the iPhone 5S' display, I'd say it's excellent in terms of colour reproduction and general effect, but there are better displays too choose from - the Sony Xperia Z2 is worth looking at, for example.
Many people will be upgrading to the iPhone 5S from the 4S, and this is one of the few areas where, extended size aside, they won't see a large amount of difference.
The sharpness is great, the colour reproduction still industry leading, but the brightness can be a little erratic for some low-contrast movies and isn't big enough for speedy typing. HD movies still look acceptable on the device, but I've seen a much more jaw-dropping effect on rival devices, such as the LG G3.
I like that Apple is leading the charge to stop screen sizes going too far in the wrong direction, but there could be something more that's done here.
Even a display with a thinner bezel would have impressed (although scaling apps might have been a problem, with is something Apple is so proud of) but I still think in the face of fierce Android opposition the iPhone 5S display could be better.