I agree it is an exciting and fresh film. A bit uneven in terms of quality, I think some of the "chapters" were better than others. I don't know if you got the same feeling, but I personally thought the ending was poorly done, as if the director did not know how to end the film. I had the feeling it dragged a bit and the final scene was just too much weirdness.
Oh dear, it was open to interpretation of course! It is weirdness but tailed with a logic.
I could tell you mine:HOLY-SHMOLY SPOILER ALERT!!
The whole film is essentially a movie within a movie.
Now, even without knowing so, an interpretation that anybody who watched it twice can at least make is that life is imitating art (in this case,the world of cinema) openly in the movie, with actors performing out in the open in a never-ending series of dramatic acts: that is at least what the corporation "Holy Motors" is. the whole bunch of stretch limos returning after a day's work signifies that a corporation pays actors to act out roles in real life, not inside a theater. Why? Because people want the dramatic life that mimics cinema. And why is this corporation "Holy"? Because it provides everyone a second life in their same life - one that is more dramatic and closer to the life they want - the life of the movies. This is what everyone else who "hires" the actor is paying for.
But the problem people find is that it does not lend in coherently with the few gaping holes if that theory is to be applied singularly. Well, it isn't to be applied in isolation because it does not explain the double-roles, the genuine deaths and the finale of the cars talking to each other. It is such heightened bizarro in the movie that signifies that nothing of what we have been witnessing all along is real, but is in a world where these bizarre things (like the actors coming back to life, and stretch limos talking) can happen repeatedly. And what can be that world within the world? - The world of movies, which creates allowance for such surrealism! It is to explain this logic that Carax slyly uses images of black-and white footage of old motion pictures randomly in the main "outer" movie which shows the same actor reminiscing about 'cinema as it used to be' as he draws the curtain open: movie theaters are long gone and dead in the real movie. What is left is where we are transported to: the impact of cinema in real life of people where everyone is acting all the time! That second part is the movie within the movie which is the bulk of the movie "Holy Motors".
I hope I made sense!
P.S: I read somewhere that it is Carax's tribute to the world of cinema, so I hope I am right somewhere.