The subpixel layout for that type of PenTile AmoLED display is quite different than how most LCD displays do it. The result is that the effective resolution is much less than 1080p, making text less crisp than it could be.

See the Display portion of Anand's review:
http://www.anandtech.com/print/10411/the-oneplus-3-review




Now mind you, my old Galaxy Nexus had a 720p AmoLED display, and I didn't mind it a nit. But since replacing that with the 1+1, my eyes have gotten used to the crisp seamless fonts and icons of the 1+1's 1080p LCD display. No going back!

Edit: I just remembered something else that was bad about the Galaxy Nexus AmoLED: way, WAY too dim. Not usable outdoors. Anand suggests the 1+3 might have a similar issue.

My 1+1 is very usable even in direct sunlight though, and Anand suggests similar brightness from the 1+3.