Over the course of about a year, I peeled through all three volumes, and enjoyed it immensely. That said, I was aware of Foote's more problematic issues as a writer of historical non-fiction, and took what I read with a grain of salt. Pros: the writing is superb and engaging, and as a narrative history, it does a great job walking a reader through the war. Cons: it is spotty in terms of accuracy in sections, Foote doesn't cite, and it is LOOOOOONG.

Foote is wonderful at painting a picture with words, and lulling a reader into the world he's talking about. His three volumes are very long and detailed, but that's because he did seem to be attempting to draw the reader into the world he was unspooling. He really takes his time developing the backgrounds of the figures he writes about, and connects all the sociopolitical dots between the events.

Most importantly, I think he does a great job writing an all-encompassing history of the event in terms of giving equal time to the north and the south. He spends near-equal time talking about Lee AND Grant, Davis AND Lincoln, etc. Now, women and minorities: they don't get as much time, but if you're looking for a surface-level history of the ACW from top to bottom, you're in luck.

Lastly (and not surprisingly), the best parts of the books are the reminisces and stories that you aren't going to find anywhere else. As OP stated, Foote doesn't really cite anything, so it's hard to know just how much of it is true, but if nothing else, these little anecdote nuggets are a hoot to read. I recall one bit early in the 1st volume when Foote writes about the early (EARLY) days of the war, when amateur generals were in charge on both sides and making extremely questionable decisions. Foote talks about a southern general who positioned a cannon well out of range of the enemy, and ordered it fired. When told that the cannon had no hope of hitting any hostile targets, the general replied that he wasn't concerned with the range, but the FEEL of it in use. Weird stuff, but you won't find it anywhere else, and some of it seems like it COULD be true.

In the end, I'd treat it like an oral history of sorts: something to get a sense of what really happened, to draw you into the event without putting all that much stock into its complete accuracy. Some of it is really, really good history (nothing new or exciting, but a damn fine retelling of events), and some of it isn't (the Stonewall Jackson sections, especially). To answer OP's question, though: I waded through it and enjoyed it immensely, so I felt it was indeed worth it.

For a more historically accurate narrative history that has stood the test of time, I'd highly recommend anything by Bruce Catton, especially the Army of the Potomac trilogy. Catton gets through all the same stuff as Foote in about 1/3 the pages (and he's a better writer). Catton is also very well regarded as a historian, and his works (many of them over 50 years old) have stood the test of time.