Unmodded Skyrim is unplayable, the companions say as much as 'Hello", "Nice weather" and "Goodbye" and have a mini quest.
They did however provide a brilliant toolkit and there are user made companions available with a lot of background and up to 9000 lines of voiced text. I wouldn't go outside in Skyrim without Vilja at my side 
I never finished the main campaign Civil War, as I am not suitable to choose sides with the racist local rebels or imperial forces who suppress and torture/kill everyone. Again, there are mods that enable you to say "F**k them all!" in the main campaign.
All the other factions are game enough to explore nearly everything, like the Dark Brotherhood (hell yes), the Thieves guild, mages guild...
Here the big difference:
You join the dark brotherhood, kill the emperor and it has nearly no impact on other stories. The town crier (was he from a mod?) will update his text and people talk about it in the world for a while, but that is it.
It is absolute not possible to finish the quest in any other way than it was intended by the developers.
In Dragon Age Origins you had several outcomes and lots of plot flags to take with you into other adventures to come.
Dragon Age 2 was quite linear for the main plot, with lots of circumstances that could be altered on how you solve things.
I haven't finished Dragon Age Inquisition yet, but it feels also very linear.
On a personal note, I prefer games with a main plot you work towards. All the side quests and content in the game should help you reach that single goal and not drift off or just finish without any impact.