[Lalaith]

People have asked about the Norse world view, optimism and hope. Not believing in a conventional afterlife does not necessarily make you a pessimist. Here's a poem from Havamal which is often quoted to demonstrate the essential Viking view of the afterlife:

Deyr fé,
deyja frændur,
deyr sjálfur ið sama;
en orðstírr
deyr aldregi,
hveim er sér góðan getur.

Deyr fé,
deyja frændur,
deyr sjálfur ið sama.
Eg veit einn,
að aldrei deyr,
dómur um dauðan hvern.

Translation: "Your cattle shall die; your kindred shall die; you yourself shall die; but the fair fame of him who has earned it never dies."
"Your cattle shall die; your kindred shall die; you yourself shall die; one thing I know which never dies: the judgment on each one dead."

Now (look Saucie, I'm on topic!) that sounds very Rohirric to me. Kind of thing Eomer might have roared on the field of Pelennor - and he never struck me as a particularly gloomy soul. The other thing I thought about, regarding the emphasis on bravery and reputation, was that Vikings did have a heaven - Valhalla. It was for men (warriors) only, they fought all day and feasted all night. They were chosen from among the bravest of the slain by the Valkyries of Odin, and it was all in preparation for the Last Battle. Theoden "returning to the halls of my fathers", perhaps?
Turin returning to kill Morgoth at the last battle of Middle earth has always felt very Norse, although I know it's not strictly canon. As does the last stand of the Men of Hithlum. So perhaps Tolkien portrayed the Rohirrim, and the Edain of the First Age, in a similar way - a noble but "young" culture, like that of the pre-Christian Vikings.
The other example of despair that springs to mind is Galadriel's Lorien Lament, but that is very different kind of despair to that of say, the men of Hithlum or Eomer in battle, it feels like a more "Renaissance" kind of intellectual despair.

Fea, in answer to your question about the sun: in Norse (and Germanic) culture, unlike Graeco/Roman, the sun is female. She is called Sol, and will be devoured by a wolf at Ragnarok, the final battle. Some people maintain that Baldur was a sun god, and others that Frey (fertility god) was, but I'm not so sure.