A really interesting idea. The guy is a kind of shapeshifter. At some point his body starts to decays, and if he touches someone, he absorbs his life and takes their appearance, and some access to their memory. In itself it's not a revolutionary idea. But the way it's treated is really original.

First he's not an alien, a spirit or any supernatural entity. He was just a nomal kid in a normal family and it just happened. He doesn't know himself where it comes from, how it works or why.
Secondly he's been living like this for a while (around a hundred years, I'm not sure), so he learned how to deal with it. How to recognize when the time comes. Painkillers make a body last longer, cocaine accelerates the decay. How to choose the next body, how to get rid of the bodies. It became a routine, just like a boring work.

And then it's almost all wasted on a stupid "love" (stalker) story. So there's this girl, he's in love with her, and each time he has a new body he goes to the bar where she spends her evenings and chat with her. In itself, not a bad idea, bt then it becomes almost the whole story and it's boring because it goes **exactly** as you would expect.
I'll still put it in a spoiler tag, but come on, every step is so obvious, nobody spent more than 2 minutes writing that.
[spoiler]
At some point, he becomes her boyfriend with one of his bodies.
He's super happy.
Body starts to decays. So he tries to explain to her.
"Yeah, so I've been going around, killing people and stealing their bodies. So almost everybody you spoke to over the past two years, that was me, yep. Also means that all these people you though you were talking to, they're dead, I killed them. But it's ok, I love you, I want to be with you."
She doesn't take it really well (no shit!).
They fight.
He accidentally kills her.
[/spoiler]

There were so many other possibles ways to go. The thriller way, because he leaves a trail of disappearing people, and the police has to catch up at some point, it could have been an interesting game. But even if at some point the police actually discovers the place where he's been hinding dozen of bodies, it goes nowhere and has almost no impact on the story. Or maybe more discoveries on his own story, trying to find where this coles from. Even flashbacks of his youth or some important moments in his life could have been great. There was **so much potential** and it's wasted in the most common way possible. Such a shame.

Ending adds a little interest, [spoiler]he finally let himself die after having killed her, but turns out he just ends up in a cocoon and rebirthes[/spoiler], but it's too little too late, it leaves more questions that should have been pursued in the movie instead of this basic plot.

Still worth seeing I guess, but it could have been so much more.