Heres whats missing or changed:

Many reviews already mention there are no challenge dungeons in this game, making all the grinding in all the chapters but the last worthless. But theres more bad news: they did not mention that all the bonus bosses in the final dungeon from other cameo FF games are gone and replaced by recycled IV bosses (including ultima weapon). And the fact that you cant farm adamantite to get adamant armor sets for the entire team, but just one set (adamantites are final rewards in challenge dungeons). Plus, you also dont get the developers office (or maybe its a different location that no ones discovered) where you could trade in items to get more goodies. One of the worst things they did was mess with the final dungeons layout. Its bad enough the tailed monsters that drop rare tails can be found in a single room in the dungeon, but whats worse is the monster shows up only in 1/4 phase of the moon. Determining which monster is where is practically impossible without a guide, which are all wrong because iOS version is different. This problem could easily be remedied with a siren that triggers rare encounters in a given room, but for some idiotic reason, sirens have been taken out of the game!!!

ZenMasterZ about FF IV: THE AFTER YEARS