IIDX is generally hard. I don't really care much for the American version that came out though. The game is supposed to come with the controller and the game itself(factory sealed anyway).
I have a jap slim PS2 that I use for IIDX and Pop'n Music.
I would say IIDX has a pretty steep learning curve, which is probably why it didn't do too well in sales here in the US. People were probably like "wtf is this?". If you play it a lot though, you'll definitely pick it up quick and get used to it. At first, you'll probably have trouble locating the keys 100%, so you'll probably miss a lot until you get used to the controller.