No, the US does a lot more than just investigate, and does not give you citizenship just for marrying someone (few places do that - most give you the right to live in the same place as your spouse, though). Going through the whole process involves something like 2 or 3 trips to whatever town has the US consulate you need to go to (a 5 hour trip for me), and in the end, and involves a lot of fees, and requires things like doctor visits, which is kind of degrading.

Bureaucracy in the US isn't all that bad for many things, but from the point of view of a potential immigrant, it can be pretty ugly. Anyone remember when they were stringing along Linus Torvalds and people raised a fuss about it?