Should have used MODERN elements instead of classical ones!
So, the storyline is... Fire and Water go on a date. Can they find a way to be compatible?
Meh.
The premise would have been 10X MORE interesting if they had gone with personifying MODERN elements (e.g. ANYTHING on the Periodic table), rather than simply use the "classical elements" of Fire, Earth, Wind, and Water. It would have allowed for far more "diversity" (I thought Pixar LOVES "diversity") with 118 DIFFERENT types of elements you could use INSTEAD of just four, and it would have been fun to play up the traits associated with each element after you anthropomorphized things like Gold, Silicon, Arsenic, Iron, Iodine, etc., etc.!
HUGE missed opportunity!