This waterfall has to be seen to be believed. I would like to clarify a few points here.
Seeing the previous reviews regarding the approach road, I would say that there's a new road & its as good as the Ring Road. The road is not yet in Google maps. If you are approaching from the east along the ring road do not turn for the first road that indicates Dettifoss as it is gravel road and without a 4 wheel drive the ride's bumpy and it might damage the car also. Travel further along the ring road and cross the river. The brand new road comes on the first right turn and it ends into a wide parking space. At the crossing there are information boards on the left side too. From the parking area, the walk to the falls goes through a sort-of rift valley and has mild ascents & descents over rocky/sandy path.
The second fact is that the present view (just across the other side) gives a better cross section of the falls. The best part from this angle is that the whole visual field is occupied by the roaring falling water, as if the whole earth in front is melting down. This can cause vertigo in some. Although, just to mention it here, most of the film-shoots have been from the older side.
We heard that many people guess that there will some bridge across the river through which they can just cross over. We learnt it the hard way. There is no bridge and you cannot get across to the other side till you go further 25 km - its not a good idea on that road. But we saw the falls from both sides and we recommend the newer road & a wider view.
And lastly, a walk upto the Hafragilfoss, about 500 mtr from the Dettifoss is truly rewarding and is definitely recommended.
It is a must visit now!!
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.