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The comparisons between these two games seems quite obvious at first glance, but then again lets not forget the details. The developers are quite insistent in their numerous videos out of Gamerscom that their new flagship will be completely different from FFXI. They plan to do this by appealing to a wider array of players across the spectrum: FFXI fans, Final Fantasy fans, MMO fans in general, and new to MMO fans. The greatest difference would be the emphasis on balancing party and solo play. To do this they have added a variety of game elements like the Armory System and Guildleves. The interpretation would be that if you wanted to be a one person wrecking crew, you could.
The following table was put together to compare FFXI to FFXIV.
You'll notice that there are plenty of places that still need answers. The idea is that comparing apples to oranges isn't possible, but if you had to, it would look something like this. The most exciting aspect is the involvement Square Enix is putting forth to get feedback from the community. What didn't work will surly be fixed, and with the theory of a longer beta period, it support the idea they want that extra community involvement.
The game may seem to be going in too many directions by appealing to a wider audience, but that could also lead to innovation. There are plenty of ways to attract a wide range of players, but if you take the core elements and property apply them, you'll have the same effect. This is currently being applied by the developers in way they are focusing on the PvE elements. By all accounts they know some may enjoy PvP, but by focusing their efforts to developing one area really well, they hope to attract both play styles.
Thanks for reading, and I hope you'll continue to follow our FFXIV coverage to launch day.