It's a good question and IMO, the answer is - It depends.
If you are just looking for a single room "streamer" or configuration then I think the answer is that they are high priced ($350 new/$200 used) compared to some of the other options out there for streamers with DACs or digital outputs. A CCA or a Raspberry Pi variant (Allo Digione, Boss, Toneboard + VIM, Digihat, etc) will get you more functionality for less money. I think Amir or Archimago (can't remember which) reasoned after measuring cheap streamers like raspberry Pi and CCA that people are wasting money buying an expensive stand alone (ie, non-dac/amp) streamer.
However if you want multi-room (especially 3 or more zones), I think Sonos is a bargain. You can get in the game with a refurbished Sonos Play for $120 and their other more upscale speakers are pretty comparable in price and quality to what other multi-zone speakers are out there (Apple HomePod, Libratone, Denon etc).
The Big Market Differentiator in my option is the mesh network that connects all of the Sonos speaker zones. I've used Airplay for 10 years and had it with the drops and the other software out there (Airfoil, Squeezebox and even Roon) that "works" with Airplay devices just couldn't cut it and ended up being worse than native airplay. Sonos almost never loses connection or synchronization between zones. I assume Sonos has a patent on the mesh speaker network since I don't think any other company offers something similar (keep me honest - I've never tried some of the other formats - Like Play-Fi or HEOS.)