When a demo is done properly, it can create a lot of buzz around an unheralded title. The early days saw Fight Night Round 3 stun 360 owners with its sharp visuals and crunching slow-mo knockout replays.
Later down the line Civilization Revolution, Lost Planet, Bioshock and Burnout Paradise all had stellar demos that did a great job of selling the game in question.
Sometimes it's too easy for developers to fall into a "here's the boss, now the demo ends" trap. Unfortunately, some developers tend to fall even further. Here are the five most disappointing demos, all notable for the fact that they've turned people off the game rather than onto it. They might be free but sometimes, you get what you pay for...
5. Battlefield 2: Modern Combat
4. Sonic The Hedgehog
3. Turning Point: Fall of Liberty
2. Too Human
1. Hour Of Victory