Thus, any packet sniffer out there (be it by a credit card thief, the NSA - who may also be credit card thieves, or anyone else) can't look for context to decide what packets to grab. There is no context.
Actually, there is the very important context of who is transmitting to whom, and when, which IPSec is giving away. Each user, therefore, might as well be the subject of a pen register.
With I2P, all they see is a stream of encrypted packets to random points and even the 'when' is obscurred (I2P users onion-route traffic for other users by default and expectation, so you can think of this protocol as marrying ideas from IPSec, Tor and Bittorrent).
That means having to decrypt absolutely everything, including DNS lookups...
Speaking of DNS lookups: Why make your addressing dependant on centralized, establishment-controlled scheme? If PKI can be subverted to let them eavesdrop, then IP addresses and DNS certainly can be as well. Addresses that operate like public keys are much better.
Its already there on your TAILS disc... try it out. ;)