Personally, I think that doing medicine as a graduate degree is much better...
After pre-U, pursuing an undergraduate degree first fis important or student's to gain experience and be accustomed to university life. Besides, this is a time if transition from pre-U to university life which some students might not be able to get used to. Moreover, at this stage of life, students are still not mature enough to cope with stress and strain of studying such a heavy subject as medicine.
On the other hand, if medicine is studied as a graduate entry course, students will have been exposed to the real world and society. This makes them more mature and society-conscious. They also gained more experience from work in the real world, enabling them to make proper judgment and reasoning, and also think more maturely.
Well, this is just my 2 cents. I'm stating this just from my point of view and observation of medical students these 2 years. Anyhow, some students really do well doing medicine at undergraduate level while some should probably take it as a graduate-level entry. It all goes down to the capability, characteristics and passion of the student involved.