Snyder's Superman is boring. Static, unflinching, inhuman. Most emotion we get is him telling Pa Kent "You're not my daddy!" and being mopey.
It's a film about the illusion of choice, whereas Gunn creates an actual choice for Superman to make.
There is no competition, really, and that's why Snyder was let go and Gunn was brought in.
That's why the new Superman is critically loved more than MoS.
Gunn's film is just the better adaptation of the character.