The biggest and really significant weakness of BTC is SHA-256, that is ASICs (which are a very genuine threat feasible for any dedicated attacker, getting a design and building a semiconductor fabrication plant can be had for a few $M). All renowned cryptographers agree that scrypt is far superior. Also the hashing algorithm can never be changed for BTC because that would require resolving the entire historical blockchain to achieve the same level of security LTC brings from the start. SHA-256 coins are rightly dead, and BTC is the only one still living off its initial and very major publicity until it will be replaced by a superior competitor (quite likely LTC or possibly PXC) just like Netscape Navigator, Yahoo Search, Friendster, Myspace, or any other generally innovative tech with execution flaws was. Doesn't take a genius to see that.

Also an imo ideal compromise between block time and network scalability (those altcoins with 60 seconds blocktimes and less couldn't ever scale to even what the BTC network is now).