Hard enough for me to convince myself to buy a game that requires at least 3, there seems to be a typo on the main page for this game.

FFG, you may want to fix that...

This was never the game for you then.  Dune is not even remotely fun with 2-3 players.  With 4 it still doesn't compare well with most good 4 player games.  It was designed to work as a six-player game, and it's fortunate it works pretty well with just five, too.  The game is all about balance of power, betrayals, etc.  Imagine playing Diplomacy with 3-4 players and you'll have an idea of what I mean.  The rules don't change but the experience falls to pieces.

That said, I don't see it as saying 5-6.  Still says 3-6 for me, and who knows, maybe FFG came up with some genius idea to make it enjoyable with fewer players.  I hope so for those who want it, so long as such changes wouldn't affect what made the game such a great 5-6 player game.

Adam said:

It was in the flash animation at the top of the game's main page.  It appears to have been altered to read "3-6" now, so it was just a typo after all.

That said, I do agree with Adam's comments.  The genius of Dune is how intrinsically political the game is, and how much control to screw around is put in the hands of the players (Truth trance, anyone?)  It's easy to mod the rules to play with as few as 2 if you want, but it's just not the same as playing with 5 or 6.  It has nothing to do with the mechanics, the thing that makes this game great is the players themselves.