Having been a fan of The Mars Volta for some time (since Deloused in the Comatorium) , and after being blown away by their previous album, The Bedlam in Goliath, I was slightly disappointed by Octahedron. While still musically brilliant, some of the energy from their recent albums seems to be missing. If you like some of the slower, more ethereal songs from the previous albums, then this should be to your liking.
Chances are, if you are a fan, then you are fairly open to 'different' music, in which case, give it a go, but approach with and open mind.