After spending a month and a half traveling across Sri Lanka, India, and Nepal I was able to see everything from ancient hilltop castles, to the sprawling Kerala backwaters, to standing right in the heart of the Himalayas. I was fortunate in Sri Lanka to exit the hill country before the massive monsoon rains arrived which caused numerous deaths, displacement, and a state of emergency. The beaches and surfing were excellent for those that do not mind long bus rides.
India is a test of patience for most people I would think. The smells, infrastructure, and culture are sure to be different for even the most seasoned traveler. That is not to say you should avoid India, just come with an appropriate attitude and open mind. The food and chai was a definite highlight, as was just seeing everyday life here. As most destinations have attractions, such as the Taj Mahal, India is an attraction simply in everyday life. The hectic cities and traffic can wear you out, but you can also see thriving local communities and markets in the seemingly never ending chaos.
Nepal was a welcome retreat from the busy life India offers. Sweeping mountain views and long treks are sure to satisfy everyone from a novice to an expert. The speed of life here is slower and the hills offer trails and areas that can only be accessed on foot, or helicopter in a medical emergency.