Asai Nagamasa really does come across as a tragic figure. He was clearly a talented general and might well have carved out quite a name for himself had he not taken the fateful step of crossing Nobunaga. Even then, he was undone - it seems to me - by simple numerical inferiority. His army fought very well at Anegawa and the victory near Otsu later that year. Yet he never mustered more then 10,000 men - and, just as Endo Naotsune had warned, their allaince with the Asakura was not to their advantage.
As an aside, I recently read that Takeda Shingen had evidently been informed that Asakura and Asai would attack the Oda lands while he was campaigning against the Tokugawa in the winter of 1572-73. Shingen defeated the Tokugawa at Mikatagahara on 6 January 1573; just two days later, while still north of Hamamatsu, word came that the Asakura had elected not to move. Shingen issued a statement condemning the Asakura's lack of will and marched back to Kai. this event is depicted in the movie "Kagemusha', although, for whatever reason, Kurosawa has it go down while Shingen was attacking Noda Castle, later that year.