There are tow that are very well-written and cover the sprawling nature of the military conflict in a concise yet informative fashion. A War To Be Won: Fighting the Second World War by Williamson Murray and Allan Millet is an operational history of WWII. It manages to cram a lot of issues (military operations, grand strategy, intelligence, logistics, military organizations) into a single volume. Another book worth checking out is Richard Overy's Why The Allies Won. It hashes out the various factors (economic, strategic, moral) that helped swing the war in the Allies' favor.

I like Robert Leckie's Delivered from Evil. It's a bit dated at this point and was always a bit more popular than scholarly, but I like its narrative style.

All Hell Let Loose - Sir Max Hastings. Anything this guy writes is worth reading.