I only know about the difficulty of DDR specifically, but I'd say that Mario Mix covers it up to about mid-Heavy. There is no equivalent to Max 300's insane difficulties or something like that but the songlist is excellent and it covers the low difficulty range well so novices can dance to any song, not just a few like in old DDRs which only had a few sub-3-feeters.
A weird thing is that the songs are kind of arranged in a progression of difficulty, so Super Hard on on of the earlier songs (defined by its place in Story Mode) will not be as hard as Super Hard on a later song. This still holds true in Free Play, that's the weird thing.
I have fun with it and I'm really, really good at DDR so I'd recommend buying it if easy-ness is your concern.
^ It is an utterly inescapable miasma of pure, mind-shattering MADNESS from which no mind can awake!