Strizh is very comfortable and service is absolutely fine!
I have travelled from Moscow to Nizhny Novgorod last week with Russian Rail and it was great! Very friendly and welcoming service and comfortable seats and beds to reach Nizhny in relaxed atmosphere. Food was good, newspaper service reminded me about German ICE, a compliment! Although rail tracks are not always the best In Russia, Strizh is so comfortable that it does not matter!