I foundation year very useful, I actually opted to do foundation (met all the requirements for starting year 1) as I didn't feel I was ready yet for starting the official degree but didn't want to be stuck doing nothing for a year!
Foundation years are designed to get you up to the level required to start the degree, some students were mature (we just have a lot of them at my Uni though) and others hadn't met the degree course requirements for year 1. For my course specifically it was aimed at improving peoples drawing skills etc as all the animation courses at my Uni are very much art based, they taught it as if you have 0 knowledge and then cover everything.
I learnt more things relevant to my degree in that single year than I did in GCSE-A Level
edit: we covered a lot of things I did in A Level art & design as foundation years are classed as level 3 (same as A Level)
If you look on the University websites and courses they should show module guides, explaining what will be taught.