Even on an IMAX screen giant battling robots gets rather dull after it goes on long enough. Maybe this isn't true if you're 17, but I'm not 17 so there you have it.
A silly, stupid, pointless plot full of holes is to be expected in a movie like this, and can be overlooked to a point. We crossed the point here.
In a few years this film will fall into the same bucket as Jurassic Park: everyone will talk about how amazing looking it was for its time, but few will actually go back and sit through 150 minutes of it again.