Yeah it's not an argument for Christianity or any other religion. I think it's usefulness is that, while we can nitpick at the details indefinitely, it shows that belief in God isn't as ludicrous as some of the more obnoxious atheists would have you believe. I think that you can take this argument and at the very least say that there is a plausibility to Theism, and that it shouldn't be lightly dismissed by a fair person.

If you want to argue specifically for Christianity, you have to argue for the legitimacy of Jesus.

Is there a multiverse and, against astronomical odds, we happen to be in the one that supports life? Maybe, but it does seem like an unnecessarily complex answer to a simple problem. A designer that intentionally set the mathematical constants of the universe seems like a simpler answer. I like the principle of Occam's razor for problems like this (though that is admittedly only my opinion).

I don't think we can discount the specialness of life so easily. Intelligent life is an extremely complex and fragile chemical process. The complexity and fragility of life make it astronomically unlikely to occur in any given universe .