My experience with Karims at nizamuddin was pretty bad. They opened at 6:30pm and started taking orders at 7:00pm onwards. Well what is the use of opening the restaurant at 6:30pm? Morover, there was nobody to attend. Even for water we have to call the waiters atleast 5 times. And the order arrived after more than 45mins. Adding to the misery even the food was not so delicious for which Karim is famous. I saw all the customers dissatisfied within my visibility range and a few complained that the food is stale, just taken out of the refrigerator and fried again.
I would recommend the Karims at Jama Masjid. At Nizamuddin its not worth the time, patience and cost.