The negative reception for this game when it was first announced was overwhelming, I think the first trailer had something like 12x more dislikes than likes on Youtube. Square Enix/Eidos made several big mistakes. First they released a teaser trailer a week before E3, leading many to believe a next-gen console/PC Deus Ex would be announced at E3, and in general over-hyping the game. Then they announced that it would be a mobile title, which annoyed people for several reasons, such as Deus Ex starting as a PC series and how bad virtual analog sticks are on touchscreens. Also, the first trailer made the game seem like an iOS exclusive, angering many Android fans, and though they later clarified that it would also come to Android, many still believe that it is an iOS exclusive because they never heard the clarification. The trailer showed that they basically just copy/pasted the interface, animations, etc. from Human Revolution, making many feel like the game was just a cash grab attempt. Also, many fans of the book were disapointed because they didn't feel like they'd be able to enjoy the story through a mobile game.
They probably could have redeemed themselves by announcing that it would be ported over to PC/XBLA/PSN, or by announcing a proper next-gen/PC Deus Ex at E3, but they failed to do so. Just a huge fiasco for Square/Eidos.