Navalny is much more than blogger. First off, he used to be a prominent member of the liberal Yabloko party, but was excluded for nationalist tendencies.
He also worked as assistant to governor of some region or something like that, i.e. has some administrative experience. He also became prominent due to his anti-corruption struggle vs. government-owned Gazprom, VTB-24, etc. whose assets are constantly being stolen by crooks.
I think, the main problem here is that very real problem of corruption, lack of any plan for the future, which Putin is showing, and lack of any serious strategy in general, is being used by neo-Yeltsins like Navalny. His political views are unclear, his goals - even less so, and his sudden rise to prominence overnight and very favourable views from the western press suppose a certain influence from the Western think tanks, who could implant a certain agent to push certain changes in Russian political life.