Milner from MBR rode it last year, video on youtube somewhere, when the magazine revisited Helvellyn this year they commented how dollywaggon was difficult and unrewarding and they looked for a different and faster route down.
I rode the down last year and found the combination of steep gradient, large steps and drainage channels too much. Once I had stopped (due to bottle going) found it hard to get going again.
Ultimately its probably not that severe for lots of riders, but I think it is a disappointment after the fun of the last few miles