Apart from midrange transparency at which they excel, there's an overall coherence to an all electrostatic set up (not using dynamic speakers for woofers), but my experience is no doubt dated. I bought my first pair of original Quad ESLs (a/k/a the '57) in 1973 and ran them in various configurations, with subs, ribbon tweets and unadorned, until about 1990, when I bought a pair of Crosby modified Quad '63s- a better overall speaker with less beamy high frequencies, more apparent bass and the ability to play louder. But, to my ears, those '63s- which had the benefit of the Crosby tweaks from the era- never achieved that see through quality of the original '57, so when I decided to restore a set, I chose to have the '57s refurbished, not the '63s.
Over the years, I've listened to others (also dated)- Dayton Wright, some huge Martin Logan (I think it might have been called a Monolith but could be wrong) driven by Jadis amps at a lovely little boutique on the Il St Louis in Paris, their early, original CLS, and going back further, double KLH 9s with Marantz tube electronics, Janzen tweeter arrays, etc. I did not hear the Soundlabs- I should, nor the Beveridge, from back in the day. I gather that the Sanders are a preferred maker these days.
I hung in with electrostats until 2006, when i switched to a horn array, one that also depends on dynamic woofers-- the Avantgarde. In some ways, a very similar experience in getting the deeper bass to cohere with an unfettered midrange. I keep the restored Quads as part of a second vintage system that is just "yummy"- perhaps a bit romantic, but oh, those old Quads- maybe I'm just lost in a nostalgic sound. The folks with the Soundlabs and Sanders might tell you that you can have it all without the shortcomings.
Interestingly, on amps, I long ran mid-power ARC amps- high quality in the day, from a Dual 75a, to a D70 mk ii, to a Classic 60 (which was part of the newer ARC sound at the time- less tubelike). The best the old Quads have sounded, though, is with the measly old pair of Quad II amps running real NOS GEC KT 66s. Within the limits of that speaker, it's the best sound I have obtained on them.
Electrostats can be addictive, even if other speakers can do some things (bass thwack, high dB) better. FWIW, I didn't confine myself to chamber music, string quartets and small jazz combos. You can hear into the music at lower volume levels. I would guess that with the right current model, large enough panels, you can come pretty close to getting it all. And perhaps, with more modern woofer technology, you can enhance them effectively without the seams-- I now run the '57s unadorned, without any tricks, mods or augmentation.
They are insensitive to side wall placement, want to be well away from the front wall (the wall behind the speaker) and at least with the Quad, were acutely sensitive to tiny adjustments in angle- no doubt due to the very beamy tweeter panel. Mine are in a relatively small room.
Viz:
https://thevinylpress.com/a-tribute-to-quad/ 
