The long-awaited deeper look at Andorian culture finally happens in "The Aenar," the concluding chapter of the Federation Trilogy.
A long time coming, especially after the first-ever expanded look at the species since the first season, as Romulans continue their secret military operations (now geared directly against the meddling Enterprise), we finally take a trip to the Andorian homeworld and encounter an albino offshoot race being used as pawns in the conflict.
That means Shran is still involved, and that makes three episodes in a row, the most sustained presence he has in the series. (As noted elsewhere, had Enterprise made it to a fifth season, he would have become a series regular.) He's easily one of the best parts of the series, and is just one reason why these episodes are worth catching.
Had Enterprise been more like Deep Space Nine, we probably would have seen more of Andorian society a long time ago, but it's still nice that we finally get there in "The Aenar" (which, by the way, is the name of that albino offshoot race).
While most of the Federation Trilogy is about figuring out how Archer finally starts the ball rolling to an interstellar alliance, this entry rests the story solely on the Andorians, which half the rest of it already had, which alternately can name these episodes the Andorian Trilogy. The Andorians, as represented by Shran, were an important part of the series, so it's great that the final season got to make some kind of statement and milestone on them.
It may also be worth reiterating that the Romulans appear in this trilogy through surrogate means, always hidden away at their own home. Historically, there was the Romulan War (which might've been featured in future seasons of Enterprise had it lasted), and then the first realization of who they really were in Kirk's day. In a way, "The Aenar" is similar to "Observer Effect" in that it has unconscious franchise echoes. The relationship between the Andorians and Aenar is similar to Romulans and Vulcans. More to chew on.
franchise * series * essential * character
Memory Alpha summary.