Bear with me here.
With the release of spore, this has become a pretty serious issue. I think a lot of the problems with people saying games are awful is because the developers show videos of the games at events like E3, people think it's amazingly cool - and then four years later when the game is actually released the graphics look outdated and the concept is a bit stale. Had the game just been released, odds are it would have had a much better reception.
Generally hype is bad. I really hope that games like Mirror's Edge don't go the same way that Assassin's Creed did (same sort of issue as spore but in a different way - amazing concept, but criticised for being a bit lacking in depth). Same with Diablo III - Blizzard are good, but then so is Maxis - people have remarkably high expectations for unreleased games, expecting them to be the next best thing.
So, would it be more prudent in some ways to just release games or to release perhaps small teaser posters rather than full on demonstrations every quarter?