It takes too long to make a transaction, there were no easy built in backups built into the wallet, you needed to download the entire block chain, while sometimes you couldn't even GET to the p2p network without hardwiring in a fallback ip, which frankly goes against the whole point. There is also the problem on non-continuous curves through out the whole thing. Every two weeks miners would get onto irc and bitch about the newest hardness level. Why is it every two weeks? That is crazy. Also, why are we running GPU cards for weeks on end just to ensure distribution. That is stupid.
This is the internet with computers, it should take less than 500 ms to confirm a transaction. It should take less than 10 seconds to install bitcoin and accept a new transfer (ie, I shouldn't have to download the entire blockchain). I shouldn't have to heat my house while ensuring the accuracy of the block chain.
The next bitcoin will address these concerns, and will be widely adopted.
Disclaimer: I made a decent amount of money speculating on Bitcoins.