Just lack of strong material. There are a few highs, but way too many lows.
She wanted to be all artsy and release her lead single with lyrics that no one understands. When you compare the lyrical content of all her albums, ARTPOP has way too many lows.
The title itself too. It doesn't help when she's going around saying "Even I don't know what ARTPOP means".
The music was underwhelming for her at this point in her career. She kept talking about the album being some "artsy" type thing that only her fans would understand and this and that, and its extremely off putting. She tried to hard to incorporate to many "hidden" truths and meaning into whats a vapid and lack-luster album.
