I've just done history AS Level with AQA!
I would be lying if I told you that it wasn't difficult... I think that out of all my AS subjects, history was the one that I had to work hardest for - particularly with the first paper* - as it involves an awful lot of memorisation and you have to be able to put these memorised facts into context and relate them to the argument effectively.
It can be a little demoralising initially because on your first essay you may only receive 5/12 (or was that just me?), but your technique and writing style really improves over the course of the year. History questions are of course more open-ended than science or maths papers although your answers still follow a formula that you become familiar with by the end. I certainly found it a tremendous change from GCSE, where I also did AQA. For example, you have to remember historiography along with individual historians' names which is never fun and essay answers are much more focused on debate rather than simple factual recall.
That said, I thoroughly enjoyed the history course and essay writing almost became second-nature by the time I'd finished my exams. Would recommend if you enjoyed history at GCSE.
Tip: Pay attention from the start. It's all relevant. Try to read a bit beyond the syllabus so that you can impress the teachers (and eventually examiners) by referencing facts that you didn't learn in class.
*Trust me, if you do the Tudors everyone is called John or Edward.