I traveled by duronto express from chennai to delhi and delhi chennai. It was a nice experience to travel non stop.
There were a few problems with the train.
1. The toilets: They suck. After a few hours of travel, water collects on the floor, making it very difficult to enter or leave the toilet without messing up your dress. The latches dont work in many toilets. The commodes overflow. The toilets are filthy within a few hours.
2....
more... Food served is bad to horrible. Food is charged for in the ticket and could be much nicer.
3. Electricity outlet, though provided near the switches for fans/lights don't work in most compartments. So one can forget charging phones.