1. the production is top-notch and at the time it was the most expensive thing ever made for TV (Tom Hanks and Spielberg used many of the same sets and other production items from Saving Private Ryan)
2. the writing is fabulous
3. the acting is fabulous (see all the actors discussed earlier)
4. the storyline is great because it follows 1 army airborne company throughout the war, and this particular company happened to be put in the absolute worst/most legendary events of the war in Europe (Normandy, Holland, Battle of the Bulge, liberating the Eagle's Nest, etc), and it's all true, right down to some of the wounds each guy received. At the time many of them were still alive and their interviews start each episode.
5. It's 10 episodes, so the character development is unprecedented for a war film.