Both are general purpose engines and can be put towards a wide variety of game genres. Out of the box, UE4's editor comes with about half a dozen templates (FPS, top-down, side-scrolling platformer etc) for rudimentary intro projects.
Unreal Engine is somewhat harder to use, but it's graphics engine is a bit closer to the cutting edge - it's the go-to engine for AAA devs these days. Unity's main user base (for people who use it to make games - some use it for academic ends, or for tech demos) tends to be the indie game scene.
They do the same job, but differ in the technical aspects and ease-of-use, and business model (though both are aiming to lower the barriers to making games), and they tend to cater to different segments of the market.
Unreal Engine is somewhat harder to use, but it's graphics engine is a bit closer to the cutting edge - it's the go-to engine for AAA devs these days. Unity's main user base (for people who use it to make games - some use it for academic ends, or for tech demos) tends to be the indie game scene.
They do the same job, but differ in the technical aspects and ease-of-use, and business model (though both are aiming to lower the barriers to making games), and they tend to cater to different segments of the market.