I would have to agree with the others that said the Amiga community is what keeps the amiga the most interesting.
After that, I would say that it is the fact that the amiga was designed by a few guys with a great idea. And there are lots of examples of hardware add-ons created by small teams. In the modern computer world that just doesn't happen anymore. One guy really can't make that big a splash. Just look at the credits for a video game and you see that it took a hundred people to make it. These days, one guy is insignificant. That is different in the amiga community. It is full of guys (and ladies) that made some big contribution without having a million dollar budget or huge design teams.
Lastly, I think that as a programmer it is entirely possible to learn every detail about the amiga (not that I am in that position). Try mastering Mac OS X or Windows XP. How many other machines give you a complete desctription of the hardware registers and all the libraries?
