The plot concerns a scientist who creates a robotic simulation of himself. There's a great deal of romantic comedy, an evil enemy scientist who wants to put together a presumably evil army of robots, some incredible action sequences, lots of fun special effects, and-- fear not-- a lengthy procession of lavish song and dance production numbers, each more surreal and ambitious than the last.
The trailer offers a glimpse of my favorite part: a bunch of robots get together to create a giant cobra. I can't for the life of me remember the context of this event, but it reminds me of that part in Shao Lin vs. Ninja where somebody blows up a giant ninja, only to see it break up into... a bunch of normal-sized ninjas!
According to its imdb trivia entry, "Endhiran" is one of most expensive movies ever made in India, shares a costume designer with the "Men in Black" series and an "action choreographer" with "Kill Bill", and is the highest-grossing Indian film of all time. And according to me, it's a pretty darn fun movie.