Promising but so so ending

Rating: 5/10 (26 July 2015)

The story goes like this: there's this "it" that follows a person and tries to kill the person. However before the person dies, he/she can pass the "it" to someone else by sleeping with someone. But if someone is killed by "it", it would come back to the previous person.
The "it" is peculiar in that when it shows up it appears as a different person each time and it can only walk, not run, towards the victim.
To make a story short, eventually one of the victim decided, with help of her friends, to fight back and try to kill "it". Their first attempt was to shoot it, but it doesn't die.
Their next attempt is to lure it into a swimming pool and electrocute it. Now why do they think electrocuting would work while bullets don't? And the way they tried to do it is funny. They throw electric appliances into the pool.
In the end, I think they managed to killed it with a gun but there's no explanation why it worked this time. Or maybe they didn't kill it and the movie has no ending. It's ambiguous.
How is this worth 7/10 on IMDb?? I feel deceived.