Saoe said:
DA2 had a good demo, then I bought the game and it ended up being crap.
You're probably the first human being I ever heard describing DA2's demo as "good".
Not even fans of the game (yes, they exist) ever dared to go that far.
Back o the topic, a common mistake from people releasing demos is this idea that you should put as little as possible in them.
No, you actually should put in a demo all that's needed to hook a player, obviously without giving away too much.
But that's very relative. For a five hours game 20 minutes of action shooting could be enough.
If your game is a huge RPG with more than 100 hours of content, on the other hand, you can be bold and put even ten hours of gameplay in your demo.
be assured that if your game is good enough, when the player will finish that demo he will crave to continue his adventure.
Let me make an example: I remember being totally sold when I played the leaked press demo of Deus EX: Human Revolution, which was all the first "act" of the game.
Now, if by any chance I had to play a demo of the same game ending end just after the starting tutorial, I wouldn't ever consider to purchase the game.
So yeah, I guess a bad demo (or a demo fro what's actually a bad game)can damage your sales, but a good one can increase them to a significant degree.
A demo is also a big deterrent for casual piracy. If a guy can just download an official demo to test how the game runs, there are good chances he won't bother with downloading an illegal copy.
But if he's "forced" to pirate the game to try it, then there are far lesser chances that he will also buy it once he's convinced it's good.