One word sums up this entire movie:
Trippy.
"Limitless" revolves around Eddie, a struggling writer with real trouble focusing on tasks. His appartment is a mess, he's got very little money, his Girlfriend just broke up with him and he suffers constantly from writers block. Then, he bumps into his Ex-wife's drug dealing Brother, who introduces him to NZT, a small, clear pill that enables the taker to access 100% of their brain power instead of the usual 20%. His life turns round dramatically. He writes his novel in four days, he makes the entire stock market fall to it's knees, learns how to play musical instruments masterfully and also casually learns to speak fluently in several different languages. But Eddie doesn't realise the dangers of this newly developed drug and is put in immediate danger, both by those around him wanting to harness the power of NZT and the drug itself.
The thing that leaps out at you is Neil Burger's masterful direction. He gave the audience a real insight into the workings of a mind influenced by narcotics, with the composition of the world around the characters being altered quite significantly throughout the film, whether it is rotating the shot so up is down and down is up, or zooming into the iconic New York City yellow cabs, just to zoom into another one, and another one, creating this incredibly effective endless feel to the films setting. Note that even simple things such as the colour scheme changes depending on the mental state of the characters. Everything becomes much brighter when they are on NZT, with everything in pin point focus, compared to the dull, out of focus characters when they are off the drug. Neil Burger. Remember that name. I think he's going to go onto great things.
Bradley Cooper also proved that he is a force to be reckoned with, and not just another "pretty faced" actor that is only hired for his looks. Cooper is a great leading man, you don't doubt his performance for a second. Robert De Niro's scenes were as great as they usually are. Not his best role, but when you've done movies such as "Taxi Driver", "Raging Bull" and "Cape Fear", I doubt anyone would be expecting this to be his best role. His character was a ruthless businessman, he played him professionally.
"Limitless" casually glossed over themes such as addiction and ambition, without making the attempt to tackle them obvious. Cooper played the part of an addict well, making the viewer feel sympathy for his position whilst still allowing them to maintain their semi-consciousness of his crushing addiction to this drug. Desperation was another theme that occurred several times throughout the course of the movie, the most notable scene it is apparent in is when Eddie needs his fix of NZT, but he cannot reach the pill and is forced to drink the blood of another human being to get a "hit".
Like Nolan and a big majority of his films, Burger has allowed the ending of "Limitless" to be ambiguous. There are also a few unanswered questions and confusing morals for the audience to debate over, but I don't want to spoil anything.
I'd give "Limitless" a rating of 5 stars and class it as one of the best films of 2011, behind greats such as "Black Swan" and "127 Hours".
P.S.
Take a closer look at that poster, see the two messages in the NYC neon posters to left and right of the two main characters, "Unlock your potential" and "Clear pill".