Now that I've seen the full PV and listened to all 3 single songs, it's time for my review!
Don't think. Feel !!! - At first I was not really thrilled with somewhat of a mature singing style of the song, but it does fit the melody quite well and over time I have grown to appreciate it much better, however it's not a type of a song that has as much replay appeal because it's not a song with a catchy chorus nor a party song. This song is also not a good live song because of the song's character, when I watched this performed at 10th live the audience was not into it as much as say the Puyopuyo song. This song won't rank among top 5 Idoling songs in my mind, but it's still a very decent single song that may have some mainstream appeal factor considering its tie-in with an anime Fairy Tail, but I wouldn't hold my breath that Idoling will finally arrive into the mainstream with this particular single.
As for the PV, I was surprisingly pleased with it, they seem to have used quite a bit of CGI, the most I've ever seen in an Idoling PV, so things are heading the right direction, however the concept is still quite simple in execution that leaves a lot of room for improvement and Idoling can keep improving on that for the next PV hopefully. I was glad that they kept the concept rather sincere instead of being comical or something, that would've totally ruined it considering how the song sounds like. The members look great in that costume, they look both hot and cool at the same time, and that's a deadly combination that always works.
恋の20連鎖!! - I never liked the first one that much, but this one sounds really good, it's very catchy without being overly cheesy, the melody really gets you pumped up and gets me energized listening to it, which also had a great reaction at 10th live. It's almost a shame that this song won't have a PV, it shouldn't cost too much to shoot one since they already have the costumes made, and using a simple setting should be more than plausible.
アルファベットでこれなんだ !? ~保健室大作戦~ - Well this song is rather laid back and casual in style which should suit the group-character of Idoling, but I just don't like the melody very much, it's just too dull for my taste. But I don't hate the song, it's just not what I would listen to constantly.