I love this series because it is a hilarious read and trying to track down the sources for the crazy stuff he sometimes says can lead in very entertaining directions.

That said, I don't think any modern historian could cite his work and have it taken seriously. And not just any modern historian, really. Here is what a review from 1939 of "The Life of Greece" says:

As an historian of Greek civilization, Will Durant can be dismissed briefly. The Life of Greece differs from other third-rate textbooks only in its few cautious pages on sex, in its striving for " style ", and in its romantic " philosophizing ".

and

Racism is naturally accompanied by the notion that it is the leader-hero who molds history. Mr. Durant reveals a deep distrust of democratic forms and a contempt for the " mob ".

and

Mr. Durant has read fairly widely, but not enough or with sufficient discrimination to avoid innumerable errors or to be able to distinguish between a wild guess and a sober judgment.

His work is certainly good for a laugh (I particularly love his discussions of sex), but neither modern historians or his contemporaries took his work seriously.

I can't really speak to his purely historical work, but his single volume history of philosophy isn't bad. I mean, it isn't great by any stretch of the imagination, but it is highly readable and is a pretty decent as a loose introduction to the subject so far as it goes. Frankly, to my knowledge there isn't really a great single volume on the subject, but Durant's book certainly isn't nearly as bad as, say, Bertrand Russell's History of Western Philosophy

Follow up question: Why are holistic "big picture" histories so out of fashion? Other than Durant and HG Wells before him, I can't think of any other examples. I realize "all of human history" is a ridiculously large topic, but then so is "all of physics," and yet there are dozens of examples of popular books that purport to summarize the entire subject for the general reader. Why not history?

Odd though, if we are finding racist tones in his books. I'll. Red to go dig up my copy of "The History of Philospphy" but I'm fairly sure, while the language is outdated, that he gives a rather rigid condemnation of racism ( pointing out I believe in the ever shifting narrative of history, in that different groups rise and fall with the passage of time and that ( in this example, if I'm recalling it correctly) also showing through example that attributes of beauty are largely subjective and partly defined of a ruling majorities own biases, and thus, any particular "truth" in race bias is largely unsubstantiated.