I don't have anything against Chennai Express, its not a bad movie but its also not a very good one either (just my opinion). It wasn't made to be a great movie, it was made to be a popular one and based on the box office figures, they succeeded. Its the same with Krish 3 and Dhoom 3.
Box office numbers aren't an ideal way to judge a good movie, it measures popularity. The hope is that it is more popular because it is a better movie but in reality it rarely if ever works out that way.
PS: Saw Drishyam a few days ago, loved it