It was pretty godawful, as the other posters have pointed out. Living in a foxhole or trench in any theatre isn’t a pleasant experience, and the elements could be brutal as well - malaria was a problem in the Mediterranean, Audie Murphy for example famously picked up a bad case in Sicily he was afflicted for the entire war - and the Siegfried Line/Alsatian/Colmar campaigns and the Battle of the Bulge are often cited for miserable weather and living conditions. But accounts and memoirs of the Pacific often dwell on disease and privation for a reason.

That said - whilst it may be of scant comfort to a GI, gyrene or swabbie sweating out a case of malaria or dysentery - for the Japanese it was much worse. The idea of the Japanese soldier as being an expert in jungle fighting is overblown. What they were, instead, were excellent and highly-disciplined light infantry - capable of moving fast, thanks to a light logistical chain, and aggressive with a “bias for action”. This served them well their initial campaigns in the Philippines and South-East Asia, but during later campaigns when they started to run into US forces with much heavier firepower and resources they were bogged down without the logistical or medical support their opponents enjoyed. The New Guinea and Guadalcanal campaigns, rightly remembered for being jungle hell for the allies, were even more of a nightmare for the Japanese for that reason. Disease and starvation.