Immediately, we noticed how stifling the train car was. After a hot hot day in Venice, scrunching into a tiny sweaty compartment did not make us happy. The car attendant indicated that there was something wrong with the air conditioning and they were working on it. She did nothing to help us get comfortable in our room or show us how to open the windows. We started messing with the windows (so did the Spanish speaking couple next to us) and we finally figured out how to open which gave some relief. Every other train car had air, so I think our attendant disappeared into a cooler car, because we didn't get much assistance from her or see her again until the end of the trip when she returned our passports. (It would have been nice to have someone show us how to stow the top bunk in the morning and turn the compartment back to seats, too.) We also found that there was no power in our outlets, so it was impossible to recharge our phones.
After 3 sweltering hours, we pulled into Milan around midnight. We heard some voices and some pounding, so someone must have tried to fix the air, but alas, no air when took off again. Finally, several hours later, things cooled off as we got farther north into the mountains and there was some cool air coming into the windows. We slept some, but it was not the first class experience I expected.
In the morning, the shared restrooms in our car were totally disgusting. There was no toilet paper and the floors were covered with water. Yuck. No one ever bothered to clean them. It was gross.
We walked down to the restaurant car - they had a breakfast with a rubbery croissant, tea or coffee in a paper cup, and a plastic bottle of juice. That was it.
For an expensive first class ticket, we got a cheap third class experience. Around 9 am we arrived in Paris and were able to depart this awful mess. So beware, if you decide to book this train - it may not be the class of service and accommodation that you expect!