First of all, I have no direct experience of game design courses, but I get the impression from interviews in Edge magazine and online, that developers are lukewarm when it comes to games design courses.
The reasons they usually give are that many of the game design courses in the UK are hampered because they can be quite good money-spinners for universities, so the pressure to set up these courses can mean that they can be brought in to being when there aren't really the staff and facilities to do it well. Also, because students can have expectations that game design is going to be non-stop fun, when it turns out that it can be hard work, and requires technical knowledge, maths, logic and so on, students can be put off and even drop out. To avoid this, some courses can go quite light on the 'tricky stuff', to try and keep their numbers up.
However, some game developers forge close links with local universities, and have a symbiotic relationship with them, whereby the developer lends the university its expertise and experience; and the university identifies the 'cream of the crop' to the developer after graduation.
I suppose the thing to ask yourself is whether the course in question is going to teach you what you need to know. I don't think there's any point doing the course and expecting the piece of paper you get at the end of it to enable you to walk in to a game design career. But if it's going to give you the skills you need, then great.
As others have said, though, you might be better off getting a degree in Computer Science, and then 'topping up' those skills with ones learned in your free time, and then put all that in to practice to get a great portfolio that shows a real passion for the job.