I've not had it, and never will... but there are a bunch of reviews out there that have an "extreme eating" appeal, and I thought I'd highlight the the AV Club's take, since it is by far the best. It's worth clicking on the link just to see what it looks like in a non Glamor Photo context. Also, how can you argue with this line?
Like grief, the Double Down is experienced in stages.If you're curious as to exactly how unhealthy it is, Nate Silver runs the numbers. Turns out it's surprisingly low in calories (relatively speaking of course), but on a bite by bite basis it's definitely got all the unhealthiness you could ever ask for.