Having read the short story, I can now compare it to the movie
Okay, so I didn't have high expectations for the movie, yet found I enjoyed it, but naturally it made me curious about Philip K. Dicks original short story the movie was based upon. I wanted to see what elements made it through, what didn't, and most importantly if there were any underlying themes or thoughts that didn't make it to the final screen.
After reading it through, I was surprised to find that the movie, all things considered, was a fairly decent adaptation. The original short story is a fun, enjoyable read that makes you think about a neat scientific concept, and the movie does close to the same thing. But to understand that opinion fully, lets start at the beginning...
The book begins with the protagonist waking in a plane flight after the contract is up (actually, I'm not quite sure of the exact form of transport, Philip had a tenancy to name all these futuristic forms of transport without giving any description of them). He thinks back and remembers signing onto the contract and is then informed by the head of the company that it is now two years later and his contract is up. The terms are similar to the movie, we pay you a lot of money for years of work that we erase your memory of.
There are some minor differences such as how much lower wage (the story is from the 50s) and memory removal (by surgury, and no one outside the company knows about it, making explaining it extra awkward), however early on I think one of the main improvements of the book over the film takes place. We see from the protagonists perspective that he was actually nervous taking on the contract (fist time he'd done something like this in the book), pondering whether it was worth losing part of his life for money and having creeping uncertainty the moment after signing the contract. This makes him a more relateable character by having understandable uncertainty about such a major thing. Naturally, the movie changed this to give minor character development in the form of the main character learning not to sell his memories because of what he loses from it. The book also doesn't have the confusing part in the movie where somehow the character swaps the contents of his personal effects for some other objects (it doesn't make sense on a couple of levels, such as why he would be allowed to do such a thing). The book has the contract allow the worker to substitute the paycheck for a set of objects that are worth less in value, naturally the protagonist is angered when he finds out he chose such an option, just like the movie. There is an implication that similar things have happened with previous workers, though they didn't take things as far as the main character.
From that point on, I found the book and the movie pretty much on par with eachother. The protagonist goes on a quest, hooks up with an attractive lady which he's with by the end of the story, and tries to go up against the company, infiltrating it's premises using stealth to get what he wants, and aided by the fact that he's got several items that he knows will assist him at vital moments. The two do diverge but mainly because the story seems to just be taking its clichés from a different era.
Overall, the movie and the book have a similar tone and theme. I know Philip K. Dick was known for very cerebral creations, that delved into human nature and existence, but this wasn't one such work. It takes the simple concept of how a simple object can become of vital importance in the right circumstance, and uses a sci-fi concept to explore the subject in a fun setting. A classic story of a man against the system that may make you think about an interesting idea, but not to be taken too seriously.