How can we make learning more like a game?

I've discovered that this is a harder question than it looks.  Games do a lot of things:

• In a good game, you learn as you go.  You may look at the manual or watch the tutorial before or during play, but many people prefer the learning to be seamlessly integrated within the game itself.  In English class, should there be a time when the teacher stands up and delivers a lecture on grammar or essay writing?
• In a game there is a clear progression from one level to the next, often culminating in a "boss mission".  In English, it's hard to design a boss mission in which you actually need everything you've learned in terms of grammar, vocabulary, essay writing etc, unless the teacher specifically makes that part of the grade.  So does having a "boss mission" still have value?
• In a game, even though there may be a logical progression between levels, there are still many choices the player makes.  The more linear the plot, though, the fewer meaningful choices you have; the looser the direction of the story, the more choices you have.  In the interest of designing a course where students feel free do choose the assignments they feel like doing ("I feel like writing today"), do you lose the linear path to the boss mission?  There are arguments that say that learning should be progressive and the students may even feel adrift without it.  A game is usually voluntary and many game designers and academics go so far as to include that in their definition.  English class is not voluntary, so is there a point to pretending that it is?  How much choice should the students have in theory... and how much are they even prepared to handle?