Conventional advice says avoid India between June and September. That advice is written for Rajasthan, and it is wrong for about half the country.
Where the rain is the point
Meghalaya is the obvious case. Cherrapunji and Mawsynram are among the wettest inhabited places on earth, and the waterfalls that make the state extraordinary only exist properly in the monsoon. Go in March and you will see a damp cliff.
Kerala is the other. The monsoon is the traditional season for Ayurvedic treatment — the humidity is considered to open the pores — and serious clinics fill up. The Western Ghats are green in a way they simply are not in February.
Where it still works
Ladakh and Spiti sit in the rain shadow and are at their peak. The Valley of Flowers in Uttarakhand only opens in July. Coastal Odisha and Goa are lush and almost empty, if you accept that swimming is off.
What to accept
Tiger parks mostly close. Mountain roads in the Ghats and the Northeast can wash out, so we build in slack. Photography needs patience. In exchange, good properties cost a third less and you will have places to yourself.
What we would book
Ten nights split between Meghalaya and Assam in July or August, or a fortnight of Kerala Ayurveda in June. Both are trips we would happily do ourselves.