The Elder Scrolls IV: Oblivion was one of the Xbox 360's first "Must Play" titles and, thanks to downloadable content, the game has proven to be an enduring favorite. The Elder Scrolls IV: Shivering Isles is the game's first major expansion, adding more than just a new dungeon or quest. Instead, the game offers up a new area to explore that is about a third of the size of the Cyrodil, a sizeable quest involving a Daedric Prince, a new major city, several small towns, new craftable armor and weapons and 500 new Achievement Points.

The expansion doesn't do much to improve Oblivion's technical visual shortcomings. The Isle's residents are just as unattractive as Cyrodil's and there are still times where grass looks like it is growing beneath your feet. Artistically, however, it pushes the game’s visuals in a completely new direction.

Nowhere is this best illustrated than when you first enter the Isles. Rather than seeing the vast new world ready for exploration, you are dumped in a black-walled room where the only thing you hear is the clicking of a metronome on a nearby desk. After agreeing to step into the Isles, the black walls explode in a flourish of dark purple and blue butterflies revealing a bright, sunlit forest.

The Isles are split into two sections, Mania and Dementia, with the look of each reflecting its name. Mania is a bright, deliriously happy place dotted with lush forests, giant multi-colored mushrooms and clear lakes. Dementia, on the other hand, is fog-filled and comprised predominantly of dead forests, ruins and swamp land that is reminiscent of the lands seen in Morrowind. This districting even carries over into the cities that populate each section. The towns on the Mania side are well-kept, while Dementia's are filthy cesspools.

Much of the same music from Oblivion is reused in Shivering Isles. While exploring, soft flute-filled music plays only to give way to deep, brassy tones during action and battle scenes. Every NPC is voiced well, though some lines do come off as still – an unfortunate byproduct of the stiff character animations during conversations. Some of the best acted lines come from Sheogorath himself, who perfectly reflects the madness of his realm. And no, even though he sounds like a certain Spongebob character, they aren't done by the same voice actor.

Unlike previous expansion content, where the new quests just show up in your journal, it takes about a day or two of in-game time before you begin to hear rumors of a strange portal that has appeared somewhere near Bravil. Once you discover the glowing door, you are informed that several adventurers have entered and either disappeared or returned insane. Upon entering the door, you learn that the Daedric Prince Sheogorath (who you may remember from previous Elder Scrolls games) is in search of a human champion to help save his realm from a force known as the Greymarch.

Your first task in the Isles is to defeat a monstrosity known as the Gatekeeper. This task involves more than simply killing him, setting the tone for several of the quests found in the expansion. While there are still a number of fetch quests and dungeon crawls, most of the quests are a little more involved than the ones found in Oblivion. For example, the Gatekeeper quest requires that you first learn about who the Gatekeeper is, then make friends with key citizens (Persuasion skills are used more often) and discover the monster’s weakness. The changes aren’t drastic, though they are tweaked enough that they are always fun and move along at a decent pace. I even found myself taking on quests that I normally wouldn’t take and exploring dungeons I would usually pass up. During my 30+ hours in the Isles, I repaired and ran a dungeon, served as an Inquisitor, acquired and kicked a drug habit, took part in a plot against nobility and even stood toe-to-toe with a god.

Another reason is that several quests, mainly those in the main storyline, involve choices that affect the game. In Oblivion, you were given choices, though these always led to the same resolution. Several quests require that you choose between Mania and Dementia, affecting how some people will see you. Even the rival blacksmiths seem to know if you have been spending too much time in another's shop. These are small things, but they go a long way toward making you feel like you are a part of the game world.

Exploration is encouraged more, thanks to new craftable armor and weapons. Throughout your adventures, you’ll come across Amber and Ore, both of which can be used to craft weapons and armor. You can also find Matrices which, when built into an item, add magical qualities. How good these items are depends on your skill levels. Creating an Amber sword with a low blade skill will produce a low-power sword while crafting that sword at a higher skill gives you a better sword. The only downside is that each armor type is only available in one type. Madness armor can only be crafted as heavy armor while Amber is only available as light armor. It isn’t a major flaw, though the option would have been nice, especially since there aren’t many new armor sets available in the expansion.

The Elder Scrolls IV: Shivering Isles, like Oblivion, levels its difficulty based on your current level. The difficulty can also be tweaked using a slider in the Options menu to help give you the exact challenge level you are looking for. When left untouched, Shivering Isles is slightly more challenging. I walked into the Isles with a level 30 character decked out in Imperial Dragon Armor with one of the top swords in Oblivion and a Blade skill of 100. The first enemy I encountered was anything but a pushover. This theme continued throughout the game, which was a good thing.

One of the great things about enemies is that some fight better in certain conditions. For instance, one group of enemies is easy to beat in dry conditions, but are absolute beasts in the rain or in water. If you are a newcomer to the game, you might want to hold off for a few levels before jumping into the Isles.

Quests require a little more work, but aren’t too difficult to figure out, though if you need help you can summon Haskill, who acts as something of an in-game FAQ, to your side at a moment’s notice.

Getting back into The Elder Scrolls IV: Shivering Isles after a short absence, I was amazed at how well thought out the game's interface is. The Quest Journal alone was enough to suck me right back into the game, since it allowed me to easily remember what I was doing the last time I played. More games, especially RPGs, should really start doing this – so, major props to the guys at Bethesda for that.

Shivering Isles sticks to the same gameplay mechanics as Oblivion, so there are no major changes or surprises if you are a returning player. In addition to the new armor and weapons included, you'll also learn a number of new, useful spells. Like many of the items in the game, which ones you learn are based on your decisions. For example, choosing to enter Mania before Dementia gives you a different blessing and bonuses.

The only major gripe I had were the mechanics behind one of the game's more interesting swords, Dawn/ Dusk Fang. Depending on the time of day, the sword changes its name and powers. On the plus side, it is a weapon that rarely needs repair or recharging since you seem to get a new instance of it every time it changes. The problem is that every change also requires that you re-equip the sword. Re-equipping isn't too hard because of the easy inventory management screen, though it does screw up things if you have everything mapped to the D-pad for quick use.

The Elder Scrolls IV: Shivering Isles is one of the more expensive pieces of downloadable content available on Live ($30), begging the question – is it worth the price? For anyone who has already sunk more hours than they care to count into Oblivion, the answer is a resounding yes. For half the price of a retail Xbox 360 game you are getting a much deeper, and longer lasting experience with a game that has already proven its worth.