I would say the main weak point of FFXIV bosses are their arenas. Every boss arena is this bland circle that you just stand in and pew pew. Where are the multiple floors, portals, unique location, etc? On top of that, I hate the design of coil. Too much orange for my taste and for Twintania to be the last fight, it isn't memorable at all. Very challenging, but nothing special in terms of style. In fact, its boss arena is even worse than others.

My last MMO was Rift and it had some epic final bosses in raids like Crucia, Regulos, Akylios, etc. You can youtube them and see for yourself. It's a shame because FFXIV's normal dungeons are actually very well designed. Why not bring similar designs to raids? Coil has a boring theme. CT is better, but still nothing special with bosses. I already can't wait for them to be done with CT/Coil storylines because I'm not a fan of their setting - unless they change them drastically in future. I hope so.