I would say that it really depends on what your moral limits are. If you are okay with your teenager playing a shooting game in a not-even-close to real world and not killing humanoids, than you are fine. Personally, I don't see an issue with it. It does not carry the same moral stigma that the Grand Theft Auto series carries.
"Is this game for Christian's". The majority of game released aren't christian games. If your asking about the "content" of the game, then yea. If you like shooting alien-like creatures and stuff in a sci-fi like world, that is. Read the content of the game and decide if it's the right one for you. It comes down to your personal taste and moral belief. As far as I know there's no huge amount of gore in this game, your just zapping stuff or shooting with a gun, or rolling into a ball. There's plenty of website available that go into the detail of games.
There's not any blood-saturated violence in this game; it's a Nintendo title after all. Secondly, you play the role of a bounty hunter whose job is to vanquish an evil alien menace. So in that sense, I'd say this game is about as anti-christian as a game where you kill Nazis.
Hey, I'm a Christian! Yes, yes I am. I love this game. It's my favorite Wii game I have.(And I have alot!) It should be rated E10+, not T, though. When you shoot stuff, sometimes yellow blobs of gunk come out, but it isn't blood. Or they might explode, or dissinigrate. In one point in the game though, in Valhalla G.F.S., there are dead troooper bodies (in their trooper uniforms!) and if you scan them it tells how they died, and if you shoot them, they dissinigrate into black ash. Sometimes there are also some creepy alien carcasses that are the same, but they look pretty creepy, even to a 13 year old. But I think that this game is good okay for Christians, and it also has almost a Christian representation. Bassically there is corruption that can take over people, if they don't controll it. It's the same with sin. Sin can take control of you're life too, if you don't make effort to stop it.
What does the statement "Is this for Christians" even mean? As opposed to "for Atheists, Muslims, Jews, Hindus, Buddhists, etc"? What would a game for those other, marginal people be like? If this is a question of violence, then do "games for atheists" revolve around being violent and immoral? Your question makes no sense unless you qualify it and explain what you're actually asking.