These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Alternative Character Interpretation: Brynhildr. In the Saga of the Volsungs she and Sigurd are a victim of Grimhild's scheme. In the Poetic Edda, Grimhild does not appear and Brynhildr decides that Sigurd is the man she wants instead of Gunnar and if she can't have him no one will and manipulates Gunnar into the conspiration to murder Sigurd.
Ending Fatigue: The massacre of the Niflungs and Gudrun's vengeance on Atli clearly form the climax of the story. Then the narrative continues to recount Gudrun's life after that event, notably the death of Svanhild and Gudrun's revenge on Jörmunrekkr. While these are dramatic events in their own right, they don't surpass what went before, and consequently come across as rather anticlimactic. The narrative seems to be aware of this and tells these events in much less detail than the preceding, but still the author obviously felt the need to include them.
Values Dissonance: During their time as outlaws in Gautland, Sigmund and Sinfjotli attack and kill people on the roads for no other reasons than to make a living and to train Sinfjotli for combat. This is told without any apparent judgment and at one time their robberies and homicides are even referred to as "famous deeds".