First of all. I know Skyrim isn't online. Secondly, I know Skyrim reminds me of alot of games, basically as far as customizing your character and doing quests aside from the main quest line. In some way, Skyrim and mainly Oblivion reminds me of Guild Wars and Guild Wars 2; also World of Warcraft. You're a random guy/girl of a random race of people who doesn't know he has the power to save the world and has no idea that he's about to make a huge difference in the world.
Each hero has a unique ability of some sort in most fantasy games. They have this thing about them that makes them unbeatable. Whether having powers they never knew they had, or being given a power.
You start out doing what any other player would do. Volumes of quests and grinding levels to get better. You may not do the main questline until you are absolutely sure, you have everything you're expecting. You might want to hold off until you're a certain level.
Now since we're not online, we can't arm up and party team the entire quest line or join guilds with our buddies. Well thats fine. However we can join factions and either choose to be good, neutral, or evil. I chose to be black at heart.
However, what makes Skyrim very close to an online RPG is that there are always quests; random radiant quests and factions or guilds that give you these. You are given the opportunity before and after slaying Alduin, of being good , neutral or evil. I don't think the good and evil spectrum has much to do with Alduin. Even evil characters kill each other because one bad guy may want to rule the world...maybe not politically but through guilds and influence over other people; and not destroy it like the other evil character would love to do. Its kind of like a territory dispute.
Also Alduin is mainly like any other villain in an online RPG. In Guild Wars, you set out to kill a God, or an undead Lich lord, or an evil Envoy like Shiro Tagachi.
Dagoth Ur was much like Shiro Tagachi. Both were Immortal and had what we call the Afflicted as well as the Undead Lich Lord bring back the undead.
Mehrunes Dagon was much like Abbadon who wanted to enslave Tamriel. Same for Alduin.
Now I may be comparing Skyrim to the Guild Wars franchise, but the stories seem to be similar.
I see the Guild Wars franchise has some in common with TES and not just Skyrim. Guild Wars 2 seems widely based on Skyrim to some degree that it takes hundreds of years after the first one. So perhaps Guilds Wars is copying of The Elder Scrolls.
Now there May not weekly updates and monthly subscription server fees. Just like any online game, the game always has main characters that are NPC's no matter who you play as or name yourself. You're always going to be a hero no matter how many rotten choices you make. In Guild Wars, you were a hero. No if's or but's about it. But you could be a horrible person to your guild mates. People could only judge you on how you were a person, and not what your character has achieved in the game. But the list goes on.