Super ostentatiously late to the party, having just bought DJ Max Fever for the PSP. After watching a few online videos I was attracted to the game because of the track list (trance, j-pop, hip-hop, jazz, etc), but I was concerned that it would be too difficult. 4-button, level seven tracks are borderline tough, so I can imagine it only gets worse from there. However, I was happy to find that (like Rock Band 2's "no fail" mode) the game allows you to press any button for any note that needs to be played, so all that's needed is good timing rather than accurate button presses.
Even with that casual-gamer feature DJ Max Fever is still seriously difficult. But your efforts are rewarded as the game has an rpg-ish feature in that you earn gold to purchase various unlockables, such as note panels, note gifs, more tracks to play, etc. If you like rhythm/music games even the slightest bit, I highly recommend you give this title a try. It makes Elite Beat Agents for the DS seem like an exercise in boredom.