It is not one shot. Finished my first dungeon ( and video 4 should be up soon ) and it's not one shot situations.
3-4 shots? Yeah definitively, but you can parry and dodge blows as well as heal and kill enemies quite fast yourself.
The only thing is about he side quests-- I believe they go on forever since they are randomly generated.. Unless you mean like ones with specific stories, such as the Dark Brotherhood.
Certain about this? Well I'll see, but I am not going to go on forever on them that's for certain.