Well the first thing I ask is... why did they attack Earth if their final version is so far away from being done? Heck, they later dedicate an entire episode to testing a prototype weapon on an uninhabited planet. This seems... reasonable. If they were testing their tunnel to Earth, they could've sent a probe. If they were testing the mini weapon's deployability, they could've sent it to attack an uninhabited world about as far away as Earth. Just think how surprised they would've been when the final version dropped in on them unannounced. Attacking a year before hand gives the humans time to.... do exactly what they did, send someone to stop them.
That said, there is some good character dialogue from Archer and Trip. Trip especially is nice and pissy over this, and understandably so. The funny thing is... this whole Xindi arc really wasn't separate from the TCW arc at all... it involved time travellers from the future trying to manipulate the past and screw with humanity. Just like the TCW. Future Guy dropped in at the beginning, Daniels dropped in now and again to help out, and it ended with... Daniels and alien Nazi's. So yeah, I never saw the difference between the two, except another side was getting involved.
The concept of Enterprise taking off to confront the threat that's going to destroy humanity does have a romantic flair for the dramatic to it, and even though they recycled the spacedock departing scene, there was whole new feeling to it this time.
As for Duras? I dunno... honestly it felt like they needed something to pad the episode out with those they threw in this loose plot end. Otherwise it had nothing to do with the story, except maybe to show this Expanse is so badass even Klingons run away from it.
Decent episode with the promise of more to come though.