Those who felt The Elder Scrolls V: Skyrim somehow wasn't big enough should make haste back to their consoles, because the first Elder Scrolls downloadable expansion has arrived, and it offers more new game content for 1600 MS points than two contemporary full-priced shooter games might manage in combination. This is DLC done properly, refreshingly. Rather than lazily flopping out six trendy new haircuts for an in-game pet, Bethesda has instead produced an honest-to-goodness old-fashioned RPG expansion pack.

The Elder Scrolls V: Dawnguard begins with subtle insertions into Skyrim's existing narrative (provided the character is over level 10): town guards mention that they have heard the ancient Dawnguard order is reforming; the odd alarming after-dark incident with a vampire in the back allies of Skyrim's towns and cities. Investigation will lead the Dragonborn to the south east corner of the world map, and through a cave to Fort Dawnguard - another entry on Skyrim's long list of impressively monolithic ancient structures.

Here, grizzled vampire-hunting veteran Isran is reforming the Dawnguard, an order of vampire-hunting warriors dedicated to protecting the realm from the vampire threat, which once again is in ascendancy. Tasked with investigating a recent vampire attack, the Dragonborn travels to the first of the expansion's many new locations, where the introduction of a new NPC character rapidly makes the situation more complicated, and leaves the player with some choices to make about just whose side they're on.

Dawnguard's well-formed and lengthy campaign structure essentially assumes the form of a secret but world-shaping war between the Dawnguard and their immortal mortal enemies. There's something of a James Bond-MI6 versus SPECTRE feel to proceedings, especially given the enjoyably M and Q-like characters found among the ranks at Fort Dawnguard, and the vampires' efforts to execute a fiendishly spectacular plan for the purpose of gaining global domination.

This narrative shape allows the expansion to blend seamlessly with the main game - while the Dragonborn might be dragged back into the Imperials versus Stormcloaks conflict again for a while, or into helping the locals of Skyrim with their bandit problems, all the while, crucial and desperate deeds are afoot in dark places. (If only you knew, Jarl Balgruuf – if only you knew.) A generous helping of new side quests, such as surreptitiously assassinating undercover operatives of the opposing side, or gathering materials and personnel for the war effort add to the sense of an ongoing off-the-radar conflict.

The two-sided, and thus, highly replayable campaign missions aren't the only new additions Dawnguard brings to the table. The Dragonborn has the opportunity to become a vampire – and not just of the common or garden variety that was already possible in Skyrim, but a Vampire Lord, able to access such powers as turning into a mist, unleashing a cloud of bats onto foes, and choking enemies from afar, Darth Vader-style.

All these powers can be reached on a new perk tree that awards points based not on levels raised (as in the main game), but on the number of enemies chowed down on, and otherwise maimed using vampiric powers. This makes the advancement of vampire skills relatively rapid. A corresponding new perk tree is also provided for werewolves, so characters coming to the expansion as lycanthropes get some extra new skills to explore as well.

However, the forces of righteousness are not helpless in the face of their powerful vampiric foes. Players can now pack (and craft, and enchant) that essential vampire hunter's weapon - a crossbow – as well as create fearsome Dragonbone weaponry, don Dawnguard armour, or hire a hulking armoured troll mercenary to accompany them on their next dungeon delve. There's also now a character in Riften who will happily perform (for a fee) Skyrim's version of plastic surgery on the player's character, allowing recustomisation of its appearance at any time.

Dawnguard even manages to improve on one of its parent game's few weak areas by including a follower character with a history and some genuine personality. The follower characters from the main game are so typically unaffected by events around them, and so repetitious in their use of stock phrases that it's very easy to start thinking of them as being little more than walking luggage racks.

The tighter scope of the expansion pack, however, has allowed Bethesda to create a companion that feels a lot more like a person, and offers considerably more context-sensitive dialogue options and actions, as well as conversation that actually extends beyond, “I am sworn to carry your burdens”. The explanations, descriptions and backstory she provides to the player while out in the field happily make this character an integral part of the over-arching story in a way that isn't always present in the main game.

Stopping Dawnguard just short of being the perfect expansion is the appearance of the odd bug, some of which are mere annoyances, and some of which will necessitate a reload of the last save, although fortunately these seem to be fairly rare. As well, the inclusion of mounted combat (now available to all Skyrim players through patch 1.6) is a nice thought, but ends up quite difficult to use, especially in close quarters. It's often easier to just get down from the horse, club that annoying frostbite spider to death, and then mount up again and carry on.

But these are minor irritants in an otherwise fantastic package. Like its parent game, Dawnguard is full of memorable moments – watching an armoured troll lumber into battle against opponents, attending an opulent and macabre banquet set within the crumbled Gothic majesty of the vampire headquarters, Castle Volkihar, or stepping into a portal to a different plane of existence, unsure of what awaits. Fans of Skyrim should almost certainly grab it in recognition of the fact that it's hard to get too much of a good thing.