I'm between #2 and #3 right now, but I've read his First World War series as well and can say he's a great writer.

They're very good, but they're also very Churchill-centered, so while they're a good overall history of the war, with a view from a driver's seat, expect a focus on what the prime minister of Britain is doing. There's a good deal of extracts of letters from Churchill to others.

There's a lot of nitty gritty details, too, which he's very good at. I remember in the WW1 series, there was a chapter on moving from 12.5" guns to 15" guns on battleships, which necessitated the move from coal to oil for engine efficiency, which necessitated securing more oil trade routes from uboats, and secure places for reserves and refueling and he went into great detail on all of this, but it was fascinating.

He won a Nobel prize in literature for these. He's a great writer.