I have been living in Kochi, Kerala for the past 6 months and I guess I can try my level best to point out the major differences in this region.
Backstory: Basically I hail from Pondicherry, One of the UT in India. And I'm basically a pure Tamil to start off.
Disclaimer: The list is going to be long. Hence, brace yourself.
So, here goes my long list of differences that I found out in Kerala compared to the place where I come from.
1. Almost every single house in my region have roofs on their top with connecting pipelines that collect rain water and lead straight to the reservoir or to a well below. Yes, I find these people very conservative of nature (The government has also implemented this to the extent that people actually follow it). People from Tamil nadu are least bothered about nature. Very few people actually do rainwater harvesting.
2. Kerala is filled with so much nature that it would literally ooze and relish with greenery everywhere whereas, in my place the trees and plants are not very dense as in Kerala. No wonder why they call it as God's Own Country.
3. In Kerala, majority of the people are Muslims and Christians whereas in Tamil Nadu Hindus are in majority.
4. People are not so social in Kerala( I don't know but that is what I felt in the area where I live). I didn't find many people who come out of their houses and interact with others. The doors(even the windows) of all houses are mostly closed. In Tamil nadu, people welcome and treat their neighbours just like their neighbours.
5. Temples in Kerala all have a roof over them. Sometimes it becomes difficult to distinguish between a house and a temple. In Tamil nadu, the temples have great architecture engraved into it with lots of idols and scriptures.
6. People from Kerala know Tamil and Hindi apart their language. So, it's easy for them to converse with everybody. People from Tamil nadu find it very hard to adapt to the language changes if they are moving out of Tamil nadu(That is how I felt during the initial days. Now I'm learning their language :) ).
7. Food ! (This list is going to be very lengthy)
Briyani (Thalappakatti) from Tamilnadu is so much enriched with the spices and masala that you could literally taste it in your first bite. In Kerala, it is Thalassery briyani which I actually don't find it quite interesting(No offense, but it feels like jeera rice with gravy inside it).
Kadala(Channa) curry everywhere ! (And I definitely love the kadala curry from Kerala)
Puttu is eaten as breakfast and dinner in Kerala. In Tamilnadu, puttu is actually a snack.
Kerala parotta has a certain essence to it. I have never eaten such soft and tastty parottas in my life (Maybe I haven't travelled much to know) .
Every dish is made out of coconut oil in Kerala. (That explains why these people have smooth and shining skin)
This is just my point of view from what I have seen so far. Contradictions can exist. But it doesn't mean that I'm showing hatred or being unfair to any of them. I'm just sharing my experiences from both places.