As someone who used to work on a computer games magazine many years ago, and who used to get paid for playing computer games all day, I've seen pretty much every sort of game around. Modern games may be way better than those of yesteryear in terms of the photorealistic graphics, but the basic gameplay is often very similar to titles of old. The same old genres persist, namely hundreds of games that involve shooting things, driving things, or killing things.
If you're partial to shooting things within the confines of your PC, but you don't like the blood and violence of modern games, take a look at Digital Paintball 2. It's an online paintball game where your only mission is to splat someone with a paint pellet. No one dies, and the scariest thing is the occasional blast of red paint.
Digital Paintball 2 is an online game, where you play amongst dozens or hundreds of other people around the world. To get started, you'll need to download the client program for Windows from http://sourceforge.net/projects/paintball2/?source=directory which is around 26 MB. It should work on everything from Windows XP onwards, including 8, and is malware-free according to Web of Trust and VirusTotal.
Once you've downloaded and installed the game, getting started is simply a matter of running the program, choosing a game to join, and then exploring the virtual environment. Move around with the cursor keys, and aim your gun by moving the mouse. Clicking the mouse button will fire a shot.
Be aware that each game has its own collection of image files that make up the playing area, so there will be a few required additional downloads each time you play a new game. You may also find that Windows asks, shortly after installation, whether you want to allow this game to communicate through the Windows Firewall in order to connect to the public game servers. It's generally OK to say yes.
For a more in-depth intro to the game, check out the video at http://www.youtube.com/watch?v=D2kqVM-inhc