I found it a bit (lot) disjointed but was kinda perfect length for me. I exepcted it to be an afterthought and found it was reasonably enjoyable in a silly way.
Good way to try out a bunch of weapons, unlock some stuff for multiplayer, see the wildly varied justification for the various levels etc.
Don't forget to play through the last level three times making different choices (see spoiler) to unlock the weapons in the multiplayer.
the three options being: give C4 to hannah; give C4 to Irish; keep C4 and let the battleship get destroyed
Ah cheers. Presumably you have to play the entire last level through each time? (there is no save point just before you make the decision is there?)