The initial taste is a touch off-putting (boozy, grainy from the rye?), but the aftertaste is pretty stellar with the flavors marrying and the vanilla bitters emerging. I did use a sugar-free Coke, which seems to leave room for additional cherry syrup flavor that I'm craving. My house bourbon and rye are both over 100 proof, so you may have a different take with standard-strength brands... I just got a bottle of Bob's Vanilla Bitters (which I can't imagine using that often), but I've been lucky with the first few cocktails I've tried it in, this one included.
Would never describe this as an Old Fashioned whatsoever, but perhaps the best Whisky and Cola variation. The Rye really takes it to another, better level.