Medieval Conquest Simulator Sandbox. The game features an amazing single-player experience as you start as a nobody and rise through conquest. The game's story is what you make it into -- you pick what happens when making every game unique. The difficulty and size of combat can be scaled based on the skill of the player.

http://indignationgaming.com/blog/mountblade-warband-starting-a-new-campaign-for-the-first-time/

The mutliplayer is more or less tacked on and shouldn't even be considered when buying this game.

Freaking scary game. This is known as a survival horror game in the sense that you will be solving puzzles, avoiding enemies, and just plain trying to stay alive. You will control actions with the mouse, meaning if you click on a rock, you then drag the mouse to pick up and move the rock. Most enemies can be avoided, although if you do get into combat, death is quite possible as weapons really don't exist. You have to use your environment to survive.

Possibly the best FPS I've ever played. As the name would suggest, realism is kept to a minimum and it's all about the action. Your character can dodge jump, double jump, use a translocator to jump around the level really fast. Your weapons are equally unrealistic and therefore fun. It supports a wide array of game modes from Deathmatch, to CTF, to Vehicle attack the enemy base, and more. It's also got over 80 professional quality custom maps that can be downloaded for free on the internet.

While it has full bot support, it's best played with other people, and while it's not the most played game in the world anymore, it's still played by some.

The free demo is cross-compatible with the main game, meaning you can join a demo server and play with players playing the free version.