After a run of slightly disappointingly derivative stories, an original tale tackling issues in the way only science fiction can, and that Star Trek always did best.
The original series was always addressing the issues of the day - prejudice, war, diversity - and here we have an AIDS allegory. Not before time, either. David Gerrold tried and failed to get The Next Generation to cover the subject, and so it's left to Enterprise.
T'Pol's determination not to stigmatise the minority adds another dimension to her character, and we really see the bond between her and the Captain grow.
Yuris's decision to speak out is another sign that the Vulcan's monolithic culture is starting to show cracks, which will play out in later episodes, and has very real parallels in our own culture. The sub-plot with Trip and Phlox's wife is light relief, and nicely makes Phlox feel more alien in an episode where the Vulcans are revealing depressingly human flaws.
If only Enterprise had produced more of these...