In his introduction to Sefer Devarim, Abarbanel poses a very simple question about this sefer: who wrote it?
Was Sefer Devarim, like the rest of the Chumash, dictated word-for-word from the Almighty to Moshe, or, did Moshe himself compose this sefer with ru'ach ha-kodesh (divine spirit, prophetic powers), much like the later prophets did (Yeshayahu, Yirmiyahu, etc.)? Since the bulk of Sefer Devarim is simply a transcript of Moshe's addresses to Benei Yisrael, one might argue that this sefer is his own creation, just as the prophets would record their prophecies.