I'm wary of it because I expect water problems to get worse as time goes on.
Most cities don't have 24/7 municipal water supply. The water comes on once or twice a week and residents have to fill it up and get by till the next time it comes. Most apartment buildings have a water tank on the roof to supply water to the building in this manner. If your building runs out before the next time the water comes back on, the building buys water from private suppliers and you see it on your next housing society (equivalent of HOA) bill. If you own a single-family home, you'll have to sort out this arrangement yourself. As the population and per capita water usage go up, this will inevitably be a harder and harder problem to solve.
Additionally, climate change predicts India to get hotter and drier (so even less water), but with more intense monsoons. A lot of the "good" places to live (Mumbai, Goa, Chennai, Cochin) are on the coast and will need to deal with rising sea levels. Mumbai has had flooding every monsoon season for the past 10 years, a combination of terrible drainage, and building encroachment on swamp lands, lakes and rivers (environmental planning takes a backseat when there's sweet sweet cash to be made).
Other issues (that I expect will eventually be resolved):
Only south Mumbai and the ministerial residence district in New Delhi have anything close to a 24/7 power guarantee. I have relatives that live in far-flung suburbs of Mumbai that have power cuts (known locally as load-shedding) lasting 6 hours a day. It's even worse in smaller cities and towns. You'll probably need to have some sort of UPS.
Road safety is a massive issue. Indian drivers are by-and-large unsafe (as evidenced by the highest fatalities per driven kilometer in the world) because the driver's licensing authority's testing is nonexistent and any joker can get a license sometimes without even needing to get behind a steering wheel. The roads are largely of poor quality; a combination of heavy monsoons, heavy traffic and (possibly) shoddy work by crooked contractors. I'm willing to bet that riding a bike in India will give you a statistically shorter lifespan than driving. Gas prices are 1.5x American gas prices, because of which many cars and buses are diesel or natural gas powered.
Another commenter wrote about property rights issues, and I concur. If you're lucky/know the right people, nothing might ever happen to your land. If you're not/encroachers know the right people, you might have bites taken out of it by someone building a small extension to their restaurant here, a little shop there. The legal system is hopelessly backlogged so good luck bringing anyone to court over things like this. Civil cases sometimes drag on for so long that all the parties in the case might be dead by the time there's a verdict (that's not hyperbole).
A lot of this sounds bleak, I know. But they are just things to consider if you're living in India long-term. The outsider-looking-in perspective of "warm weather, cheap healthcare, live like a king" needs to be tempered with some of the realities also. And a lot of the problems I've pointed out apply to other Western expat retirement destinations (Phillipines, Thailand or Indonesia).