To be perfectly honest, I think the main contributing factor that made FFXIV an unmitigated disaster was that it is an online title and everyone should know how FFXI was not as well received because it was also an online title.
But again FFXIII also has seen it's share of harsh criticism mostly due to the fact of the lack of exploration and extreme linear progression and character interaction was mostly exclusive to just your own party members with very few significant NPCs. Most of the series conventions thrown out the window such as the removal of most statistical values leaving only HP, STR, MAG which in turn gave less depth to the combat and building your characters. There is also the issue that Tetsuya Nomura behind the game and every single FF game in which he had a major involvement he has never done a single title that takes place during a medieval era or was flavored with strong western or European designs or locales.
FFVII, VIII, X, and XIII are all FF games in which Nomura had a major influence as character artist and art direction and not a single one of these games had that medieval appeal of the series earliest installments or the more recent non-Nomura titles such as FFIX and FFXII which both titles felt completely different in terms of style and art direction which also affected the types of characters and locales present in the game.
The last and probably most predominate reason why I feel that the FF series is rapidly losing touch with it's fanbase is the fact that each game in the series does something different the previous game before it. Be it the Junction System from FF8, or Materia from FF7, or even the License Board in FF12. The only true constant in the FF series is that something will change in some shape or form. However there has been so much change the last couple of games that there very little to be recognized that the series is based on.
Take example of the Dragon Quest series for example. If you put Dragon Quest 1 along side Dragon Quest 8 or even 9 and compare the original title with the more recent one you can easily see comparisons and similarities to be had between the two.
However if you take FF1 and compare it with FF13, there is almost little to no recognition to be had between the two and one could almost think both games are from two completely different series.
I want that cohesiveness that gives the Final Fantasy games a recognizable image to return to. A level of familiarity somewhat.
I just want another FF title along the lines of something like FF6 or FF9. A massive adventure with some freedom of exploration, a conventional leveling and growth system, a medieval or steampunk setting filled with Knights and Sorcery in a traditional single player package. This is my hopes for the next idea single player FF game.
I just hope because FF14 used a medieval setting and was a failure doesn't doom future single player installments from trying such more classic FF approach.
And before it is stated "Why not just play one of the older games then if you want that then"
Because I want an entirely NEW game, with NEW characters, and NEW enemies, with it's own story and unique locales, but a modernized take on the medieval and classic FF formula, not a rehash of an old game to redundancy.