Lucy
Aside from being scientifically inaccurate (you already use 100% of your brain, duh) this movie is also just plain bad. The anticlimactic conclusion is just her leaving it all behind. You would think a supermind genius would have something a little more creative to offer...
Gone Girl
Some people consider this a perfect movie, but the ending falls flat for others. When Amy returns back to her husband as if nothing has happened, he and the audience was shocked. However, the idea that he would stay with his psycho wife instead of running away with the baby is a bit insane.