If you're looking to make a serious investment into learning the language, you may want to consider getting
Elementary Japanese by Hasegawa. This is the book that they use here at Berkeley (I had to deal with it in a thick reader form before) and I definitely came out of my first year of Japanese here feeling like I learned a whole damn lot. It pretty much hits on the all the major topics any good first year college Japanese book should.
We've never used Genki here, so I'm always lost when talking to my friends from other colleges about Japanese. We do use Intermediate Japanese though.
I've always thought that they teach the -masu form before (usually) the plain form because they don't want you to go out into Japan and basically speak rudely to everyone there and make a problem out of yourself. Of course, if you're bold enough to go to a foreign country and speak in their language only after a year of training, then more power to you.
Jam it back in, in the dark.
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Rollins