What I've listed here are the absolutely essential episodes of this season though, because it's so serialized, you're still going to be missing some of the through-line. When I first watched season three, I was really disconcerted about the direction the show had taken. Watching it this time, I don't find so much fault in it. I still don't like Dark Archer or the rest of chronically brooding characters and I desperately miss the sense of exploration and wide-eyed wonder we got in the first two seasons. I suppose I'll write more about this in an Enterprise Sum-Up
After experiencing their first run-in with the dangerous anomalies of the Delphic Expanse, some serious jerks board Enterprise and Archer goes all Adama on the one jerk they managed to capture. This leads the crew to a ginormous, mysterious sphere.
Archer tracks a component of the Xindi weapon to the Arborial Xindi colony that's producing it only to find that things aren't as he expected. Additionally, this episode has some interesting Xindi history, a new lemur friend for Archer, and we get to learn all about the lost Avian Xindi sub-species.
3- The Council:
Archer's decided to stop being such a brooding bastard and try to make peace with the Xindi. He appeals to their council (with the very competent Hoshi at his side) and things start looking up. But some people are just determined to be complete wads. (I'm looking at you, ya lizard jerks)
While T'Pol and Tucker try to dismantle one of the spheres, Archer makes a plea with the Aquatics to help him go after the stolen Xindi weapon. You get some really cool Aquatic alien stuff as well. Their ships are basically flying fish tanks.
5- Zero Hour:
The season finale. Nuff said.
Honestly, these aren't really runners up. They're my favorite episodes of the season but you don't HAVE to watch them to get the story. They're just good episodes.
This is the "one time this amazing, tragic thing happened in another timeline" episode of Enterprise. Archer's brain gets infected by some anomaly parasites. That means he can't remember anything past a few hours and he and T'pol end up chilling together for thirty years while humanity is destroyed. It gets me right in the feels. Every time.
Starfleet crews have been visiting Old West Space Towns since forever but this one is a nice take on it. Some aliens (who are totally not the aliens from Stargate) picked up some humans from earth way back when and used them for slave labor (again--totally not Stargate). By the time Enterprise catches up with them, the humans have rebelled and it's the alien species who are being mistreated and oppressed. It's an interesting take on an old idea. Bonus points for :
Aaron Pierce (Glenn Morshower) showing up as a cantankerous, tough Old West sheriff.
Everyone getting dressed up like they belong there.