It fails at its own premise

Rating: 6/10 (4 August 2014)

I'm a reviewer who has no problem suspending disbelief for the most outrageous premises. As someone with a former career in neurosurgery, I didn't even find this premise (increasing brain usage) more outrageous than others.
To get this out of the way, here's the gist on the main premise points:

people use 10% of the brain capacity: note that it says 'capacity'. It doesn't refer to the debunked myth that people have unused brain areas. We use all areas of the brain, even if not at the same time. The movie claims we aren't using the entire processing capacity of the brain in the way that if we open 10000 browser windows we are using both the main CPU and the integrated coprocessor in our computer ... however not at their full computing power. It's a fact that our brain has limits (for example, why can't we read the plate number of a car moving at 200mph? the image does hit our retinas, the information is there, but the brain lacks the processing power to process and store the quickly changing information) which some people can overcome by focused training.

people use 10% of the brain capacity: now on to the 10%. In order to claim a percentage, you need to have gaged the full process. It means that to asses 10% you also need to know what 100% looks like. But the movie makes a point of not even knowing that. Then where does the 10% come from?

the mythical drug: even if admitting something like that, there's still a problem. Why would a drug linked to developing the body still forced an already developed adult into further development? Why is that development limited to the brain and not other body parts? Why is it focused on that? The movie fails to make sense in its own universe.

Other than that, who can say 'no' to Scarlett Johannson participating in blowing up cites other than New York?
The movie is mildly entertaining as an action movie, but even if you can suspend your disbelief at the basic premise, the movie breaks its own logic so often and so severely that it's difficult to stay on track and accept the events. The Expendables is way much better at that.