Equestria Girls is one of those movies I know are bad, but i can't help loving.
The story is terrible, the romantic subplot is awkward and lifeless, the ending is rushed, you've heard all these reasons before.
The one, main thing I found redeemable about the movie is that I find the idea of Sunset Shimmer's redemption interesting.
Not the way it was executed, but the idea that a villainous character gets turned around and essentially becomes the Twilight Sparkle of that dimension, i.e. being the central friend among the mane 6, is fascinating to me.
It's like Twilight's story, but with a backstory of having been evil/villainous.