The two-year old, Samsung Galaxy S4 is finally getting its dose of Lollipop. The Spark variant of the Galaxy S4 got the update a month ago, but the update was pulled for some unknown reason. Likely due to some bugs. However, it appears that the update is headed out the door right now, so many of you should be seeing it pretty soon. It's actually rolling out for both variants. The regular Galaxy S4 is getting build L720VPUGOD2 and the Spark Galaxy S4 is getting L720TVPUCOD2.
The Changelog is actually pretty slim, just showing that the update brings the device to Android 5.0 Lollipop and brings Factory Reset Protection to the device. So it doesn't appear to be bringing the new version of Touchwiz, which isn't actually a surprise. As that usually doesn't happen. It's just another way for Samsung to talk you into upgrading. The update will likely bring in some bug fixes and performance enhancements too - not steroids though. As every update does this, whether it be an OTA or an app update.
You can head into Settings > About Phone > System Updates > Check for System Updates and see if you can pull down the Lollipop update not. It'll likely be rolling out over the next few days. If you really can't wait, you can also download Kies from Samsung's site and install the update manually.
The Galaxy S4 was announced back in 2013, and was a pretty popular device. Although every Samsung device is pretty popular. It was one of the first flagships to actually launch with the latest version of Android - which at the time was Android 4.2 Jelly Bean. It was one of just a few devices to feature the Qualcomm Snapdragon 600 processor as well - the only other mainstream device with it was the HTC One M7, as the Snapdragon 800 was available a few months later and actually made its way into the Galaxy Note 2. Up until the Galaxy S6, the Galaxy S4 was the most popular Android device of all time. Although the Galaxy S6 will likely beat it, judging by early sales.