Ambrose isn't a bad writer - Infanteer means he's a bad researcher.
And, come to that, he's not a stellar writer, either.
Band of Brothers, for example, was mostly ok - except for one truly bizarre page in which Ambrose asserts - without a single fact in evidence, a single source or quote to back him up - that the US Army won WW II because it was morally superior to the Germans, and that having a democratically elected government back home made the difference. My jaw hit the ground when I read it.
The US Army was actually more dictatorially run than the German Army in WW II, so the military certainly didn't reflect that "democracy beats all" attitude that Ambrose wraps himself up in.
I'm inclined to give Ambrose a pass on the severe criticisms of plagiarism (which are true enough), and I realize he is "history-lite" which is cool too, since he introduced so many people to WW II history. And he is right about that entire generation of people, not just in the US, but all over the world, who answered their nations' call.
But among historians, he really doesn't have as high a standing as so many other luminaries. He chose his path, and I think he was comfortable with it and was in fact good at what he did - mass producing readable, inspiring history that was aimed at a wide audience and more interested in effect that in establishing facts.