A decent episode that gives a good glimpse into the character of Shran, the Andorian Commander that has been a recurring character throughout the run of Enterprise.
As Trek is known for doing, many characters, even minor ones at times, have varying depths to them, some that are not revealed until the time is just right. Such has been the case of Shran.
In the beginning, he was basically a bully character. It seemed he was only there to be a thorn in the Vulcans' collective side. However, as he continued to appear, his character has grown (all of his growth basically in Season 2's excellent "Cease Fire"). Shran plays the role of a noble, moral man forced to work within a corrupt system. This especially is brought to light in "Proving Ground."
Although it is implied in "later" series that Humans and Andorians become fast allies (each founding members of the Federation), that has not come to pass in the time of Enterprise. The Andorian government is seeking to take advantage of Earth's tragedy by assisting the Enterprise crew in its search for the Xindi weapon, only to steal the prototype they manage to steal from the Xindi together. Shran is under orders to return the prototype to Andoria to be used as a failsafe against the Vulcans.
Shran, although he does not agree with this tactic, is obligated to follow his orders. However, Shran urges the Andorian government to seek an alliance with the Humans because he sees the potential in Humans and realizes what a valuable ally they would be. His government does not agree, rather looking for the quick solution to their war with Vulcan. However, even though he eventually loses the prototype due to Archer's unwillingness to let it get used for the Andorian's ultimate purposes, he still manages to find a way to try to help foster future cooperation between Andoria and Earth by slipping Archer important scans of the Xindi weapon taken before it was destroyed.
This is the type of story that Deep Space Nine was known for. "Proving Ground" wasn't nearly as deep as some similar DS9 episodes, but still brought back a lot of the excitement that those earlier episodes kindled. And character development, even that of a secondary character that has only appeared a total of three times in the series so far, is always welcomed, especially when it is done in a superior way.
So, "Proving Ground" was not necessarily the best Enterprise episode to date, but it was definitely one of the better ones.