[Rumil]

I've always thought that it was a mark of Tolkien's mastery as a storyteller that the early Shire chapters are comparatively lighthearted in what you might call 'tone' (I guess there's probably a technical expression), but as the fortunes of the fellowship ebb and flow the tone alters with the situation.

For me the most marked contrast is between the Shire chapters and Mordor. The Mordor chapters I find almost exhausting to read, which I imagine may have been Tolkien's intent; to put the reader through, in a miniscule fashion, the torments of Sam and Frodo.

Using the 'translator conceit' one must remember that the depressing Mordor chapters were written by Frodo, and must therefore reflect his dark memories of that perilous journey. One can contrast this with the Rohan and Gondor chapters, which must mostly have been based on the memories of Merry and Pippin and are therefore considerably jauntier.

Other sections which strike me as different are naturally, Tom Bombadil (I seem to remember an old thread on this - regarding faerie etc??), then the contrast in pace when Frodo is struggling through the Trollshaws.