It was ok for just 2 hours of explosions and Megan Fox running in slo-mo, but as soon as you start to think about it for more than 5 seconds the poor plot starts killing it.
What was the point of the AllSpark in the second one? They get it, the Decepticons try to get it from Megan, but why? It seems they ultimately forget about it later.
I'm also lost why they were trying to have the "survival of the race", when it is obvious that the AllSpark still works in slivers.
I thought they were after the information in the Allspark (the location of the key thing), and once they realized the information was in Sam's mind they started chasing him? But that of course begs the question, why couldn't they just get that info from the spark sliver they stole from the military base? Eh, plot holes...