One of my very favourite things about PC gaming is the amazing modding community for games like Skyrim. Thousands of users spend hundreds of thousands of hours improving, beautifying, expanding, tweaking, and overhauling the game, driven only by passion and a desire to make a great game even greater, and add something of value to the community.
Sometimes the mods are tiny little tweaks, while other times they are astoundingly complex and professional endeavours that put Bethesda's original effort to shame. One mod adds much more variety and subtlety to the whole game's weather system, while others add much needed complexity to the enemy and animal AI. Boris Vorontsov's ENB mod greatly improves the lighting system, and even adds Screen Space Indirect Lighting, an effect that apparently has never been seen before in games. IndigoNeko expanded on ENB and added a fantastic Depth of Field implementation - complete with camera-style Bokeh light distortion - that he claims is the best Depth of Field ever seen in games (and he's probably right - it's wonderful).
I have some 100 mods installed in my version of Skyrim, and the game looks, sounds, and plays better than ever. Over the weekend, I finally got to contribute to the community with a mod of my own. Several things about the animal footstep sounds in Skyrim have always annoyed me (eg. rabbits are too loud, spiders sound ridiculous, foxes sound like miniature horses), so I've made a mod that improves them: Better Animal Footsteps.