I personally think this movie is EXTREMELY underrated. its a good movie. the fight scenes are epic, the cast is epic and Jean is EPIC. yes there are some major issues with the screen writing and plot- but you have to understand this movie went through some major reshoots- which are expensive.
One criticism i would give is that the story isn't very well explained. If u haven't read the comics or seen some youtube videos before hand you wouldn't understand exactly whats going on.
like why did jean behave the way she did? why could she not control her emotions? what did Charles do to her? and the biggest one- what even is the Phoenix force?
overall i think this movie is definitely above 6- maybe even a 6.5.