There are more superhero movies that get the final act wrong than right:
First Avenger's fist fight
Iron Man vs Iron Monger
Winter Soldier's unnecessary Helicarrier splosions
Man of Steel's interminable Zod battle
Suicide Squad's horrible final fight
BvS's climax as a whole
Age of Ultron's endless mook-waves
Logan's big fight ending
Really every Nolan final confrontation.
None of these are the best part of movie.
Sure Ares is cheesy and looks low-budget as fuck, but I don't hold that against the movie as a whole.