In terms of overall game-play, Skyrim stays pretty close to the system Oblivion used. You roam a giant open-world map, revealing new locations to explore as go. Along the way you receive quests that you can complete at your own leisure. Therein lies the danger of this game: it is easy to get distracted and veer off from your goals and before you know it you've wasted twenty hours just trying to level up your blacksmithing or collect ingredients. I have already sunk 126 hours into this game, completing most of the main quests, and there's still the urge to keep playing. I think I "only" managed to log about 95 hours in Oblivion.
But, this isn't just a re-skinning of Oblivion. There have been many improvements not the least of which was removing the scaling-up the enemy difficulty as your character advanced. It's good to actually feel more powerful as you gain more and more levels rather than having to fight uber-powerful rats throughout the entire game. In addition, the dual-wielding controls feel a bit more natural now but the game's inventory system, although improved, was still clumsy enough to force me to install the SkyUI mod to fix it.
The graphical improvements are notable especially in terms of character animation. It's not near the level of polish as some other recent games I've played like Tomb Raider, but it manages to be a pretty realistic world to explore with tons of details and vistas to discover.
I found the main quest line to be not terribly interesting. The world is on the verge of ending because of a reemergence of ancient dragons. You must stop them, yadda yadda. At first I tried to immerse myself in the lore by reading every tome I discovered, but this got boring really quick. I suppose an Elder Scrolls lore obsessed player might think otherwise, but text info-dumps are just not a good way to reveal a fantasy universe in a video game. But, as my hours of playing will attest to, a riveting story is not the only way to keep players hooked. The exploration, the character building and loot collection are really what make this game so addicting and excellent.