Dawnguard gives you every reason to dust off your copy of Skyrim.
Dawnguard adds another "main event" to Skyrim. An ancient group of vampire hunters known as the Dawnguard are being reformed as an ancient family of vampires seek to fulfill a prophecy foretold in the Elder Scrolls with the player being put in the center of it all. Do you join the Dawnguard and kick flying man-bat ass or do you throw in with the aristocratic vampires and gain new power in the process? Dawnguard will take you to new places, both in Skyrim and beyond. And all along the way you're treated to an immersive story with enjoyable characters and rich in lore of the world. There are twists and turns, what the player originally believed may not be what comes to fruition.
But Dawnguard doesn't just add this "main event", there are other things added in just for the fun of it. The player can now craft Dragonbone weapons which are the strongest weapons in the game, vampires as an enemy the player can encounter in the game world have been overhauled sporting their own armor, clothing, and bestial servants such as hounds and gargoyles, and of course, the Vampire Lord complete with perk tree and Werewolf perk tree flesh this DLC out and will have you playing beyond the projected 10-20 hours playing around with the Vampire Lord and Werewolf powers and exploring new places making it more than worth it to shell out the $20 asking price.
And although it seems like perfection, Dawnguard unfortunately suffers from a problem but I cannot describe it without spoiling it for everyone else, and of course the run of the mill glitches that the engine faces are no stranger to the new content, areas suffer from pop in, follower AI is just as horrendous, ec cetera. But for everything that it offers and considering the tall order that's put on the engine, it's easy to forgive these shortcomings and enjoy the newest addition to Skyrim.