Hi,
I'm a ex student of RWMCD ( just part time though) and I have to tell you that it is really good. It has a really good theatre design department - I was a Music student though, so can't really offer any more info on that.
Life in Cardiff is amazing - it is a very cultural city, has a brilliant shopping centre (4th in the UK), has amazing transport links, has a waterfront and plenty of beaches within public transport distance, and is generally a very relaxed and postivie place to live.