We've been to Le Ciel de Paris twice in the last few years.
The first time for a 40th birthday was perfect. Great food, a table by the window, attentive service and a perfect view as the sun set over Paris.
The second time for lunch, a couple of years later in 2013, the food was not as good as we remembered it, the service was a little more 'haphazard' and we had to fight for our pre-booked window table.
Go just once for the view; the image above was taken from the viewing platform just above the restaurant in the direction the restaurant faces.
It's not really worth going unless you can get a table by the window. To make sure you do, book online with as much notice as possible and then call them to confirm a window table. Ask them to confirm your request by email.