vulnerability to hackers, high fees and not being accepted as a payment form... it would take years before people start accepting bitcoins as one of the accepted form of payment globally
I think the developer of bitcoin have a strong security to prevent the hacking of this coin, it will not work in the market of 9 years almost if the problem is hacking this coin.
For me the one biggest disadvantage is the legalization of this coin, it is banned to the other countries, and it is legal to the other. If this coin did not accepted to all countries the volume of bitcoin did not increase which may result of low price. People want to earn big profit in easy way and now the bitcoin is one choice. My point is if this coin banned in some countries maybe some user hate the bitcoin.