If we're not talking Ludwig van Beethoven or Johann Chrysostom Wolfgang Amadeus Mozart [had to put their full names as they are as impressive as their music] alot of modern mucisians are terrid and pale in comparison.
I'm no the biggest fan of country/blue grass, but it isn't bad, and this Chris Thile guy is pretty pretty epyx... but every genre has their "geniuses".
Thom Yorke from Radiohead or Jón ?Jónsi? Þór Birgisson from Sigur ros could battle over the alternative-rock title for all eternity with the third contender being "Godspeed you black emperor!" which is the most unmainstream alternative post/prog/orchestral/rock group ever, they have no structure or single leader with a line up ranging from one guy to a mini orchestra of about 24 members, and they're so interesting...
Another "group" that could be classed as "genius", and also fall into the post-rock pigeon hole are Cult of Luna.
Something wholey awesome and less progressive, more grungey is Queen Adreena.
Kyo from Dir en Grey has to be one of the most interesting and intreguing lyricists ever.
Steve Vai is a god on the guitar.
Johnny C's Cannon D on the guitar is genius.
Though they're both so blandley metal.
More mainstream Matt Belamy from Muse is damn impressive.
Hell eminem sometimes feels more like a poet rather than a rapper... sometimes.
The peramiters here are too vague as anyone will just spout their favourite mucisians with little real basis to call them a genius, as I must admit I have done so just a little, but all of them, minus eminem to be completely completely honest, could for their own merit be classed as "geniuses" in their own right.