Minecraft has its charms, but let's face it, it's one ugly video game. There are tweaks you can use to improve things a little, but nothing like this mod that improves things a lot.
This video is from Sonic Ether's Unbelievable Shaders, a mod that adds effects (not just improved textures) to the game like realistic water, reflections and some gorgeous lighting.
Know that this mod is for use with actual gameplay, unlike, say, those awesome Game of Thrones Minecraft vids, which were fancied up outside of the game.
You can grab the mod at the link below.