One of the main Marines in the Pacific was Eugene EB Sledge, who was on the mortar team with Snafu. He wrote the book The Old Breed, which may be the best book I have read on the Pacific battles.
I have read many quotes that have said the Marines fighting in the Pacific had it much worse than the Army in Europe. The Marines had to face an enemy, as you said, who fought to the death, not many surrendered. Also they had all the diseases like Malaria etc.... to contend with.
The Tarawa assault was the worst percentage-wise. It was not as large-scale as Normandy, but the percentage of deaths was horrific. The enemy had months to prepare and the bombardment prior to the assault did not do much damage to the machine gun pits. They also put many blockades in the water and as the amphibious boats went around the blockades it led them directly into the line of fire.
Peleliu was similar, horrible losses.
Then when we landed on Iwo Jima there was barely any resistance. We brought all our tanks and jeeps up to the beach and started to feel pretty secure. About 3 hours after the assault the enemy let us have it with both barrels. They had men up on the volcano communicating with the artillery (after practicing hitting targets for months) and just about took us down. They were very smart changing up their strategy. We were very close to having to try and get the men back off the island.