The reviewer slightly misquotes a line from Gimme, Gimme, Gimme as "Won't somebody help me chase these shadows away". As we all know, it's "the shadows", not "these shadows". He also says, "For everyone else, you can make fun of ABBA all you want, but its songs are fiendishly difficult to play and sing; I spent many miserable evenings trying to learn to bang out those minor keys on my Casio". In fact, most ABBA songs are not difficult to play. I play ABBA songs on the organ all the time. But I'll admit the chorus of Slipping Through My Fingers is surprisingly tricky until you get the hang of it.
I don't know about playing OR singing but I think the consensus is that ABBA songs are indeed difficult to SING.
That's my perception, anyway. I'd imagine they are also difficult to adequately play to some extent too, what with all the layers and layers. Having said that, i think I missed my vocation as I can pick out Lay All Your Love On Me on the piano. I'm clearly an undiscovered genius.