There have been several general complaints about this episode:
-The Students being too harsh in asking and making the situation worse
-Dolores saving the day 
-Ruining Rarity and Rainbow save for the last third of the episode, hinting at the writer for not knowing how they act.

First of all, in real life, a student when he doesn´t know, his ignorance raises up questions and sometimes, they feel hungry for more knowledge. There is no conformity because he looks for something else to learn besides the usual lessons. And sometimes, by not being used to the usual vicious circle between the experts of knowing everything, they ask uncomfortable things at times that break molds. That´s what happened with the plot device. The students feel like the fandom asking why Rarity and Rainbow are together (it would be more fitting if it were a ship). They got the responses from Rarity Investigates and Sonic Rainboom (episode callbacks by the way) but they wanted the actual proof in front of their faces. 

About Dolores saving the day. As much as we meme her bridges over here and analyze her in a more relaxed way in comparison, no, Dolores doesn´t save the day. She just serves as a medium to make them understand between each other, point out the problem and set up the final test along with Spike and Twilight. That´s it but she is not the central point but a supportive character.

And now, we are getting with the root of this episode. Rainbow and Rarity actually collide in terms of taste and here it is why I love the most: they actually have time for themselves despite all the things they have to do, it´s time just for them, no obstacles between them and they are encouraged to do what they usually would do in the daily life very clearly, so there is no biased friendship between them nor any fake action from their personality in any special circumstance. Just them, even if the students and Twilight are watching.

The humor is sassy from Rarity´s part and Rainbow actually complains like the usual cunt she is when she is shopping with Rarity. And the humor from it, I found it funny or enjoyable, call me crazy. The two things that are fair criticisms from this episode is that this should have aired earlier in S2 or S3 and that the "no friends anymore" was a bit over the top and childish. Besides that, I don´t see anything else.

Berrow actually does care and she shows what she knows the best, put the plot for a book fan club in the middle of it, the zone she knows the most (including Daring Do obviously). It served to pay off with the last third. That theft was clearly fake but it was made for strictly for them. The title references it, the end is not what matters but the relationship between you and your friend and that´s the actual objective of that quest.

They go like the old times for a simple quest and rediscover how they can appreciate each other despite their differences and tastes. This is like Uncommon Bond but applied to these two main characters. Friendships get consumed over time and don´t know how they are there at some point. 

A few fans said that this episode ruined Raridash. I don´t believe that´s true at all, the episode reinforces it because they have accepted each other without anything in the middle. It´s true that this should have aired earlier but we haven´t had many episode dedicated for these two together. In fact, it fixes the complaint of the mane 6 being friends by force and destiny. This one delivers the actual opposite, Rainbow and Rarity act like actual friends and despite arriving late in the game, they have left the room open for those who love to see them together.

Basically, an episode I didn´t expect to love so much and continued my enjoyment. It may have an average writing but like Surf and or Turf, the episodes I consider the best may not the be the popular masterpiece choices.