Every Tamil film (Well almost) has just one basic story boy meets girl, falls in love, faces his villain and lives with the heroine happily ever after.
Enthiran starts with Rajni the scientist perfecting his creation an android robot that looks like him, talks like him etc. Aishwarya is calling Rajni, who ignores all her calls, it later turns out they're already going steady. (Oops where's our love story?)
Rajni presents his creation the robot to widespread acclaim; he stated aim being to give the technology to the Indian Army so as to reduce loss of human life. But, his professor and the boss of the Robotics Bureau refuse to certify his creation stating that it's just an 'idiotic machine that has no feelings'. We are also shown the professor's other side where he's trying to sell his own imperfect robots to foreign terrorist organisations (Ah, we have our villain! So all the scenes from the trailer would mean it's gonna be Indian robot vs. foreign terrorists? Yum!)
So Scientist Rajni gives feelings and hormones programming to Robot Rajni (Arghh!) and the Robot does some good deeds which earn him the required certification. But along the way Aishwarya kisses the Robot once and the Robot falls in love with her (GOD!) The Robot even dances with Aishwarya, steps which Rajni couldn't have been managed even when he was 20! (Shankar effect!)
The Robot fails the Indian Army evaluation because he starts talking about love peace etc in front of senior army officers. In a fit of rage Rajni destroys the Robot and dumps him in garbage.
Post interval, the villain rescues the robot re-assembles him and gives him an extra red chip that turns him evil. The Robot starts creating more Robots like itself, and soon we have hundreds of Rajni clones who start committing multiple crimes, Aishwarya is kidnapped during her marriage, hundreds of policemen are killed along the way and Robot Rajni starts trying to woo Aishwarya! The rest of the movie is about how the scientist defeats his creation and rescues the damsel in distress.
In the climax when Rajni disables all the Robot clones and removes the red chip from Robot Rajni, the Robot immediately realises all his mistakes (Perplexing stupidity from the movie maker!) As for the poor villain, we learn that he was murdered by the Robot Rajni soon after the interval itself.
The songs are shot spectacularly and there's a lot of graphics thrown in where Shankar excels and one too many forgettable Robot songs where Rajni excels with his Robotic dances moves :P Rajni looks younger than in Sivaji! Aishwarya has been made to look older?? Rajni excels in the negative role!
I'm sure Rajni's pull and the marketing might of the Sun Network would've already ensured the return of investment and maybe a big hit. Shankar has spent 150 Crores to take a world class movie with a typical Tamil movie story line, if only he had spent a little more time on the story than the budget...