I used it a couple of times as my Barsoom campaign wound up. I liked it, though it takes a few run-throughs to really understand how it works.
Very useful way of handling large-scale combats, and for setting up "non-standard" combats -- one of the climactic battles on Barsoom involved sort of mental struggles against an invading race of godlike creatures and I used Narrative Combat to abstract the battle away from hit points and AoO's. It was fun and worked out well.
But I still don't feel like I've got a good handle on how it works.
Glad I bought it, though. It's a good addition to any DM's toolbox.