Here are the screens from my first "game" built in UE4. It is technically a game but not particularly impressive. Since it is the first game I've ever built I'm pretty happy with how it turned out.
Here's a video of the gameplay
I, last minute, changed the name to be "Pathogen Hunter" since that was more in-line with what the game is about... shooting pathogens out of the bloodstream. Your goal is to shoot the pathogens (the green blobs) out of the bloodstream. If you miss fire and hit the patient too many times you loose. If you shoot enough pathogens to score 1,000 points, you win!. Technically, that's all you need to have a "game". Losing screen Winning screen
From the build in UE4. It's just a BSP tube with a particle emitter that showers down red blood "cells". A HUD overlay is used for the scoring and the crosshairs. The gameplay mode blueprint The level blueprint