One of the things you have to realize is the difference in the two fights. In the Pacific, the Marines started fighting in 1942 and the war for them didn't end until late 1945. In addition, they were fighting an enemy that refused to surrender and often booby trapped themselves to kill as many as possible before they died. Not to mention the tough climates in the Pacific, from blazing heat and torrential rain. The Pacific fights tore up the Marines and you really see the fatigue and, to a degree, the hopelessness (in terms of thinking they were going to die) of the Marines as the war drags on. This gives the Pacific a much different mood. Especially since the more bleak the war gets for the Japanese, the more desperately the Japanese fight.

By contrast, in Band of Brothers, Easy Corp only were in "combat operations" for about a year, from June 1944 to May 2, 1945 (when Germany officially surrenders). And the worst of the fight was only about 6 or 7 months, as after the Battle of the Bulge the Germans knew they would lose the war and they started giving up. So, the last few months in Band of Brothers, the tone lightens as Easy Company can see the end of the war coming and believe they will make it home alive.

I think, in many ways, the two series do a good job of showing the differences of the war in the Pacific and in Europe.