In the Cataclysm expansion, WoW had an underwater zone that was horrible!
In my opinion, it was a pain in the backside to judge depth when trying to loot bodies or collect items. Trying to swim the depths of the various areas within the zone was also painfully boring and tedious.
I'm not sure how it would work in FF, but in WoW, I thought the underwater zone wasn't fun at all.
Just one man's opinion.
It was easier if you went to first person mode.
Blizzard may have gotten mixed reviews for the execution of movement in Vashj'ir, but it was a beautiful zone with an awesome concept. I'll suffer through learning how to move in a 3D environment if I get something innovative and interesting in return.
I thought it was one of the most original things they had done. The storyline was really REALLY good and after you got your "sea legs" navigating wasn't so bad. I just wish that the Abyssal Seahorse was usable in normal water. It was such a great concept relegated forever to memory and maybe the occasional alt.
In XI there was a collection of zones colloquially referred to as "sea" and I would have loved to have been able to explore underneath the surface there.