Crosmando: To be honest, the only one I've ever seen was "The World at War (1973)", and I'd like to see some more. Any good ideas? I'd prefer some with good factual in-depth information rather than being too bombastic and simplistic.
I have to say, IMHO the World At War is probably the gold standard for World War II documentary series. To be honest, I've seen so much modern-day sensationalistic History Channel/TLC bombast that it's almost bled everything else out.
I do vaguely remember seeing Battlefield on PBS, and World War II: Behind Closed Doors from the BBC, both of which were pretty good. I've also heard a lot of good things about Blood Upon The Snow: Russia's War.
The Discovery Channel in Canada used to also air an aviation-themed series called Wings, profiling famous Allied aircraft, but it later branched out into Wings of the Luftwaffe (viewing the airwar from the German perspective) and Wings of the Red Star (which focused on some famed Russian WWII aircraft like the IL-2).
Finally, if you really liked The World At War and don't mind spending a bit of coin ($5.99 USD), I
really recommend Hardcore History's
Ghosts of the Ostfront podcast series, where Dan Carlin takes his very distinctive style of examining the human angle of war, and focuses it on the Eastern Front - each of his podcast episodes are several hours long. There's a great preview of it on YouTube here:
https://www.youtube.com/watch?v=upAzM5Mduvw