I'm coming to the end of my second year at university doing psychology. It is a very mixed subject and i've yet to find a student who likes all areas of Psychology. Much of it is quite Philosophical, learning the debates and arguments behind behaviour and learning. However there are heavy statistics involved in psychology with writing report, learning things like the bell curve were no fun for me. There are also the element of studying the regions and functioning of the brain, which is very clinical and involves remembering complex names.
At Alevels you'll be just glancing over all of these areas. Most likely doing developmental, cognitive (memory and learning), obidence, brain regions and perhaps some freud and motivation (Maslow).
Although the areas of psychology are very mixed, i do enjoy doing the subject. Is it hard? That really depends on what kind of person you are, much of it comes natural to me, i like to find arguments in essays, be critical and analyse, but i know people who are more interested in strictly factual information and find it hard to bring in a debate in a scientific way.
The research you'd be likely to come across in Alevel would be; Pavlov, Skinner, case of Little Albert, Piaget, Milgram, Zimbardo, Ash, Bowlby, Freud, Loftus.
I'd recommend you read the cases of Little Albert, Kitty Genovese (bystander theory), Milgram (very interesting study), and Zimbardo. They are what i consider to be the most interesting classic psychology studies.