This would be a pretty standard promotion, giving something fun away that reinforces and builds desire for the upcoming salable product, but there's more hooks here than just that.
Within the mini-game, there are several chances to unlock items that can be downloaded and used in the larger, yet-to-be-released version. So now, the promotion goes from something standard to being a bit stronger. Not only is there more incentive to play through the entire mini-game, which is essentially a big ad for their product, but they've built a decent way to measure ROI on the mini-game. Anyone who downloads the unlocked items from the Web-game obviously ended up buying the end product, so it becomes a bit easier to make assumptions about how effective the promotion was.
What clinched this promotion for me though, besides all the swords and planning out spell talent trees I mean, was how they tied one of the unlockable items to filling out a series of three surveys, spaced out over the course of the mini-game. You play the game for a little, then answer a short survey about what you think of it so far, and also answer a few general customer-data questions, like what your favorite games are, your age and birth date, etc.
To sum things up, EA created a polished, fun promotion that is not only a great ad for their upcoming product, but also cleverly wove ROI-metrics in that reinforce the main promotion of playing through the game. AND, they managed to tack gathering customer data onto it besides.
Given all of the above, it would be hard to argue that Dragon Age Journeys isn't a well-designed promotion, but what can we take away from its methodology? Obviously promotional product distributors won't be re-enacting it literally, since it was a fully digital promotion, but in the abstract, I feel there are a lot of lessons here. Since this post is already a million words too long though, I think I'll go for the nutshell summation instead.