Yes, the only thing that marks a resemblence to the other FF's, is that there are:
- Chocobo's, Cactuars, Moogles <-- Different sorts of animals
- Someone is named Cid, mostly a sea/airpirate.
- Summons like Shiva, Ifrit and Bahamut
- Several diffirent fiends like bomb, Tonberry etc.
- Other smaller details that i don't remember.
The rest, like world, setting, characters, story, gameplay, etc is changed between each installment. Thus, making it possible for a FFXXX without getting tedious.
The only direct sequel was FFX-2 to the original FFX (but they even changed the gameplay between those two).