K or K Project as known by the majority of people has SO many things good about it. Sure it's only 13 episodes long but it's 13 episodes of pure epicness. You might not understand the story from the beginning but you have to watch the whole thing to understand it. The plot is very well made and the characters are all unique and different. And don't get me started on the graphics either, easily the best graphics I've seen on ANY anime I've watched so far. The only complaint I may have about it is the rushed plot. In the manga it seemed more slow and easygoing but the anime was a little too fast paced. But it's still greatness.
So if you're looking for an anime that includes A LOT of action, a GREAT plot, AWESOME characters, KICKASS powers and a TON of epicness, K is where you should go.