Make sure the wallpaper is sized for the S4, and don't compare android to crappy iOS. When you only allow one phone and one tablet it is easy to make apps and wallpapers. There are 100's of different android phones and tablets, screen sizes and shapes, so making a universal wallpaper is a little harder to do.
Phones & Tablets: Galaxy S4, Galaxy Note 8", Evo 4g LTE, Evo 3D, Acer Iconia A500, Samsung Galaxy Tab 2 10.1, Ipad 2, Nabi 2,
Rom: Rooted Stock Odexed, Hotspot Mod, Xposed, Wanum, several other xposed tweaks