Call it post-rock, post-prog, new ambient, art-rock or whatever you like, this song (and many other ones from this Icelandic band) isn't so far from our old dear prog. Hoppípolla (something like "Hopping into Puddles"), in particular, has a strong symphonic accent, with its dramatic crescendos and the perfect fusion of all instruments in a fluctuating, visionary wall of sound.
The album "Takk..." has a wonderful cover... hasn't it ?
I like the childish mood of the track, its Nordic, nostalgic taste, the smart passages from the loudest to the quietest moments. Most of all, I like the band's maniacal attention to details: volume, vocal effects, instruments choice... all sounds perfect, even the funny, original video with the old people acting like children. So, call this music as you like, I add it to my prog collection anyhow.