For those who haven't played it yet, here's a Facebook link that gives you a code from the official DS FB page. I'm not sure if the offer is still valid though.
Anyway, the game is a mess. What I liked about Dead Space 2 is how much of an amazing hybrid it was between a third person shooter and survival horror game. In Dead Space 3 though, they add so many unnecessary components to the game, that it kind of ceases in being a hybrid anymore The game is a plain third person shooter, based on the demo. Fact. It starts out in this "mysterious snowy place" and tries to build some kind of atmosphere, considering it's also probably the beginning of the game, but it shortly turns into a cover shooter with unnecessary co-op and setpieces. Although it's good in that aspect, that's not why I find Dead Space appealing. Games like Resident Evil 5 took a similar approach, but still had that thrilling rush permeating Resi 4 when fighting the enemies. In fact, Dead Space 3 is very similar to Resi 6, in the way that they both are stuck in what they're trying to do. Dead Space 3 gives you a lot of ammo, as you fight just 2-3 enemies on screen, and this becomes even more unnecessary with a co-op partner. Resi 6 gives you almost no ammo and also acts likes a third person shooter, because it also pretends its still like Resi 4.
In conclusion, you should all play the demo and see for yourself. My verdict is a rent, although I'd probably be buying it if there wasn't so many other games in February. I wanna hope this was just a terrible demo, and the actual game will have more of the atmosphere that define Dead Space. The upgrade system is pretty cool. And besides, Resident Evil 6 is still a good game.