When I was a wannabe film director I was going to use this in a movie.

It is very questionable that this is really by Ockeghem.  You will look in vain for anything resembling this piece from the same period.  It is known that he wrote a Deo Gratias for many voices, it was lost for a while and then suddenly turned up...  But what if it's a forgery?  It does have a repetitive trance effect that makes it sound very modern and Philip Glass-like.

Something that strikes me about it is that it sounds very forlorn.  The text is "Deo gratias" but the melody is so desolate that it sounds to me almost sarcastic.  Listening to this almost instantly puts me into a kind of doomy nostalgic state.  It seems to revel in pain.  To me this evokes the lost souls crying out from hell with profound sadness for what they've lost.  But I can  see how others would hear it differently.  To some it may just be pretty, to me it is like distilled melancholy.  

Check out my favorite nugget from pre-Renaissance polyphony, Sicut Lilium inter Spinas by Clemens non Papa.  That melody just so perfectly captures Mary, it actually sounds like a rose opening.  A lot more cheery in my opinion.