Great is going too far but this is popular for its lead character who ppl can't help but root for, the nice art, and it's really palatable for ppl who aren't normally into yuri. The big thing is that this is easy for anyone to get into. It's not like those yuri or yaoi with excessive sex scenes and fan service that may turn ppl away. Girl friends and tamen de gushi also achieve this.
And don't forget Fluttering Feelings.
Considering all the hype revolving this series earlier in the year I figured it would be more interesting and deep. I don't really read Yuri so I have nothing to compare it to within the genre, but if this is considered "great" then I'm going to assume Yuri is generally weak. that being said, the supporting characters are cute enough to have kept me interested this far (Ch.19) and will probably continue reading exclusively for them