I just watched this on Rai2, dubbed in Italian. And I would have been okay with something much less interesting, given it's merely a TV film.
This is pretty close to a gem in many aspects. Feeding so many conflicting possibilities over a very simple mystery and keeping the interest alive is essential in filmmaking, and they have done that perfectly well.
Usually, such scripts are constructed in such a way that you get the clues early on. And if you know that nothing you are fed is pointless (there is point to being misled, too) then you have a fair chance of understanding how things will be wrapped up.
The good thing with this film is, it is not constructed in that mainstream fashion. Just like Quentin Tarantino emphasizes, it steals away from the art of narrating a story to be devoid of major surprises. Most of the time we watch patterns instead of being driven away by stories.
"The Inexistent Friend" conceals its true theme while entertaining the viewer with mysteries and enigmas that barely touch on the surprise of the finale.
Was the finale great? Did it end on a high note? I won't comment on this. Not just because I have doubts to whether it was rewarding enough, but also because I don't think it matters that much, not after a successful run of emotions till that point.
Style matters, and this is one stylish little thriller with strange and unexpected enough of a resolution which you may or may not get on board with.
