It's anything but long ago that Epic Games released their latest update on the Unreal 4 engine. Doing so they also released a demo game that is based on it offering some eyecandy and meanwhile you can download the 1 Gigabyte demo file from our download section.
Making the thing run on your computer isn't too easy, since you have to extract the files to a folder and then edit the settings INI file. In there you specify things like the resolution and quite a few others. Other than that you need to install VC++ 2013 runtime an then run the demo from the correct batch file. If you mind, there is a 32 bit as well as a 64 bit executable. Closing the demo happens by hitting Alt+F4. If you care to find out how well your rig performs in this demo you'll have to install Fraps or something similar.