This is about as close to a perfect game as I have played. The action is great, the characters and the world feel very much alive, and each play through can be unique.
The best part, however, is that, after finishing the original, I've discovered the venerable 1.13 Mod. It has evolved over the years, thanks to the great community, and has far outgrown the game's original specifications. The mod allows you to control many aspects of the game, significantly improves graphics, and substantially expands the already impressive arsenal. (Due to ongoing development, there's something new popping up every few months.)