I really enjoyed the first half of Koekoi. It was your typical high school shoujo manga style dorama but the paperbag head brought made it different enough to be fresh and I was looking forward to what Koekoi would do with it.
I was completely devastated when Karata Erika suddenly left the show. Romance doramas are about delaying the inevitable but making it fun and she and the President made it fun.
The second half of Koekoi descended into standard shoujo manga fare with everyone liking someone else and seemed to have no ideas on how to capitalise on Matsubara-kun's paper head.
The show added the super boring and unnecessary childhood friend. Karata Erika as the seemingly perfect student had much more potential because they could have played around with her keeping up appearances.
The only fun thing in the middle episodes was seeing Matsubara-kun in panic mode and act more like a real person instead of this rigid robot.
I basically watched the second half of Koekoi while playing my 3DS because its was so generic and predictable including the lines.
Good thing the episodes are only 20 minutes but they should have just reduced it to 10 episodes and cut out all the fat.
Ultimately Koekoi is an ok series that did not fulfill its potential and is best watched in the background.