The food is good and fairly authentic. They not only have ‘Bengali’ food but they also have other typically (tastewise) ‘Calcutta’ food items such as Mughlai, Chinese and Club food (continental).
The ambience is very nice too. The interiors are fairly classy and they have done it up with Calcutta photographs (Satyajit Ray, old Calcutta buildings, etc), artefacts from old Calcutta houses (gramophones, oil lamps and porcelain fountains), old Bengali books and of course the rickshaw outside the door. I have taken my in laws, office colleagues, other non Bengali friends there and they all seem to like the place.
I have a fairly standard menu which I order when I am entertaining there. I start with the fish fry – crumb fried bhetki. This is a big hit amongst all who have tried it. The fish is very fresh and each bite is a delightfully juicy one. They serve it with the Bengali mustard dip, Kasundi. Adding a bit of lime to it adds to the taste. It is easily one of the most mouth watering fish dishes that I have ever had. 
I then follow it up with the classic combination luchi and chholar daal. They make excellent, fluffy, soft luchis (puris) at Oh Calcutta. I really treasure them as the only person I know who makes such good luchis is my grandmother in Calcutta. In fact I used to survive on my grandmother’s luchi and chholar daal when I had first come to India as a kid. She still makes if for the wife and me when we go to Calcutta. I sometimes order alur dom too which they make pretty well. The wife and my pa in law love it.
I then follow it with rice and fish (rohu) in mustard curry. I choose this as mustard curry is a typically Bengali dish. They make it very well here. The taste is sharper and more pungent than the toned down version that I make at home for the wife.
I make a variation to this menu when I am with my in laws. They love prawns. So I substitute the fish curry with prawns malai curry. This is a coconut based, Bengali, curry. They make it very well at Oh Calcutta and the prawns are fairly fresh. The prawn malai curry, over the years, has helped convince my in laws that their daughter did not make a bad choice by marrying me.
I feel that this menu – fish fry, luchi chholar dal/ alu dam, fish/ prawn curry rice, followed by sweets gives a flavour of a well rounded Bengali meal.
Some of my other favourites there are kosha manghso (mutton in a thick, brown gravy), biriyani (Calcutta style – well flavoured and dry and mochar ghonto (a dish made with banana flowers, coconut bits and little potato pieces).
I love the complementary alu kabli that they serve. Reminds me of the phucka stuffings from Calcutta. My pa in law is a big fan of it and could make a full meal out of it.
There are some, especially Bengalis, who find Oh Calcutta to be expensive. The menu that I described costs Rupees one thousand for two people. I think the price is fine given that it is the only Bengali fine dining restaurant in Bombay, the ambiance is classy, the food is authentic, fresh and tasty and the service is friendly and competent.
Oh Calcutta has diversified to cities like Delhi and Calcutta and I believe it is quite popular there too.
PS: On hearing that I am writing about Oh Calcutta my mom in law sent the following SMS: BETKI AND MALAI CURRY MUST GET 5
