This topic has come up many times and it appears we have different definition of chemistry. I thought perhaps it would be a good idea to discuss this issue more openly and see if some sort of consensus builds.
For some the pre-requiste for chemistry is that the couple should look physically look good together.
For me it is whether the actors are able to light up the spark that defines their characters relationship. It is immaterial whether it is antagonistic relationship, or a friendly one or a potential lovers. Basically it is - Can the viewers love seeing the two characters engage with one another.
I feel yes. With Rishi and Indira, I can feel their relationship viscerally. I may or may not like SV's or RP's phyiscal attributes individually or together, but I "get" their relationship. Their chemistry makes me "get" their unspoken communication, read thousands of words into a one second gesture etc.
There are many "in your face example" as well as subtle examples of their chemistry.
One of me favorite of the former kind was right after their first confession when Rishi was asking for a kiss and saying " aur ye bakwas mein kiss ke sath karoon".
An example of subtle exhibition of their chemistry was in a recent episode where Indira has Mandira in her lap and is comforting her. We have Rishi looking in from the window of the room. Indira has her back to him, but it is as if she senses his presence and unwillingly is getting comfort from it. We get Rishi's pain at Indira's pain. No one spoke anything. The scene lasted less than a minute. But so much was communicated.
There are some physical attributes of both Rati Pandey and Sumit Vats that I really, really dislike. But such is their talent, and the talent of CVs that I am forced to look past the unsavory bits and fall in love with the characters and their story. That is chemistry for me
Humphery Bogart was really challenged in the looks department. But he had excellent chemsitry with some of the most beautiful women in hollywood in those days - Lauren Bacall and Ingrid Bergman. Who can forget Casablanca! In recent past we have Woody Allen with Diane Keaton and Mia Farrow.
So for me, looks are important, but more so the characters and how they mesh with one another. That is chemistry
Please feel free to define what you think of is "chemistry"