All Quiet On The Western Front. Small, graphic and cuts to the chase
Stalingrad, and Berlin Downfall - Beevor. Everyone should read these, scale of cruelty and fanantisicm holds no bounds, shocking.
Band Of brothers, Pegasus Bridge, D-Day - Ambrose
Monte Cassino - Matthew Parker.
Life & Fate - Vassily Grossman. WWII version of war and peace. Its long but doesn't feel like it, written by a bloke who saw it all on the Eastern front all the way to Berlin. imo (and most historians think) the best fiction written on WWII. Some passages in there really get under the skin. More about people than actual battles as such.
Tbh there are lots but read some reviews on the book sellers sites we all know about, in sure there are plenty of other sites for references.