The Retina Display
Even though the Retina Display was more of an iPhone 4 feature, iOS 4 did bring support for the Retina Display to both users and developers. Developers had the chance to improve their apps and create beautiful-looking games thanks to the iPhone displaying twice as many pixels as previous models. Users could now enjoy videos, apps, and games with higher quality than ever before. Not to mention, this new display and software paved the way to the even more impressive display technology we enjoy today.