Well they're dance music so I guess the dark theme is my own interpretation
Not necessarily. Mille Regretz is actually a French chanson, a polyphonic vocal genre of medieval origin which is characterized by the use of so called 'formes fixes', consisting of complex patterns of repetition of poetic verses (with refrain) fixed in different specific forms (chief among them the ballade, rondeau and virelai). Those chansons were not dance pieces, and are mostly malinconic in nature (which i believe is the word you were looking for).
The number of chansons (along with their foreign counterparts, particularly those of Italian origin) written during the middle ages (and early renaissance) is vast, but alas, not well represented in recordings, both in quantity or quality.
That said, there are still many notable exceptions out there which i think will probably be of your satisfaction.
My first recommendation is a newly released collection of chansons by Gilles Binchois performed by the Bjon Schmelzer ensemble
which i think is one of the greatest recordings made to date for this type of repertory. Binchois is probably the last truly great master of this form, though there are many other great examples from all the foremost renaissance composers.
Next, Le vray remede damour
, a collection of songs composed by Guillaume de Machaut, arguably, the first master of this genre, is another seminal centerpiece for this type of music. This one employs a plethora of different instrumental combinations which results in a greater array of colors compared to the usual viol performances (albeit this was usually the instrument of choice, after the human voice of course).
Matteo da Perugia (also known as 'Perusio'), possibly the greatest of Italian representatives is also another great choice, particularly this recording performed by the great Huelgas Ensemble
. Da Perugia is actually a member of the so called 'Ars Subtilior', a group of chansonniers
who focused on all sorts of complex rhythmical patterns and explorations, in effect making this the 'avant-garde' of medieval times.
Aside from Mille Regretz, Josquin put out a decent number of chansons, many of which can be found in this recording by the Ensemble Janequin
. While the performance is excellent, the ensemble made a few flawed decisions first by cutting out all the repeats and second by setting some of the songs without voice, which recent research suggests was never really the case as previously assumed (Actually, the Machaut disc i mentioned above share some of the same problems but the results work so well it actually works quit well, plus they leave plenty of space for the some of the songs to breath). It's too bad because the melodies are really beautiful, as customary with Josquin. Hopefully some of the more recent ensembles, particularly the Bjon Schmelzer will pick this up and give the music full consideration.
I think this ought to suffice as an introduction, let me know if you are interested in more recommendations.