Yes, I'm a second year pharm student so I can give you an idea. I'm not on BOS too much now because second year's so intense but I do try to come on at least once a month now. What everyone's said so far is true, and jb_nc's comment that it's a "waste of a year" I agree with, depending on how you look at it.
Prior knowledge...um, GAMSAT is mainly first year/second year uni sciences in bio and chem (with year 12 physics) so regardless of what degree you do as long as it's science based should be fine because they all cover the same thing during that period. So med science, science, pharmacy....anything, really.
Work involved--first year is honeymoon year. Second year is hardest. Third year...no idea but people I've talked to about third years they know have a variety of opinions on this. Fourth year is the easiest because it's all practicals, and they do want you to pass--you'll be too expensive to fail by this stage.
Career opportunities--your local chemist shop, hospital pharmacy, or research, teaching in the pharmaceutical industry.
Chances of getting in--well, we've had some physiology lecturers (shared around with normal physiology subjects and from the medicine faculty) and they say that there's always a constant trickle of pharmacy graduates in there so it's really what you make of it.
It's a good degree to get into that will assure you of a decent career should you fail to make medicine, unlike medical science where I've heard first hand that all 150 second years are applying either for med or dentistry and don't really have the option of failing because no-one wants to do research (the only thing the degree really prepares you for).
Please feel free to post or PM me, but please do not expect a prompt reply as I mentioned above, second year's quite intense.