To compare "Band of Brothers" with "The Pacific" in like terms is not possible, in my opinion, since "Band of Brothers" is a story about a single unit, it's formation, training, and deployments of this unit and the interpersonal relationships formed within the unit throughout the War versus "The Pacific" which broadens the scope of the war in the Pacific between different individuals, their training within their units, their unit deployments, and their interpersonal relationship with the war, rather than with the individuals within their unit. These are two very different stories from two very different Theaters of Operations, fighting two very different fanatical enemies.
I have viewed each of the two series (I own them both) several times and I think "The Pacific" is underrated because it did not follow the same storyline as "Band of Brothers". Where "Band of Brothers" shows the unique bonding and warmth formed between men who train and fight together through adversity, "The Pacific" shows the callousness an individual adopts for individual survival through repeated exposure to an enemy who will not surrender, who fights to the death, and who has little regard for life as we westerners knew it. "The Pacific" also introduces the mindset of young men post Pearl Harbor, who feel a need to enlist to do their share of fighting and not be left to explain why they did not, or could not, fight.
Just some thoughts....