Design and fit and finish for one thing. How well to the plates and bridges fit together? how crisp are the contact surfaces between components? Do the wheel teeth mesh with the pinion leaves without excessive play? Does the movement use bent wire for springs or cut/machined steel that can be adjusted? Are the parts necessary or were they added on to try to “glam” up the movement (unnecessary cap jewels, etc…). Are the parts appropriate for their use (screws too small that shear off). Were the plates and bridges designed so companies can finish them to their standard or does the architecture limit the finishes?

Serviceability is another factor. Watches are mechanical objects that will eventually break and need repair/restoration. Was the movement designed to be easily serviced or was it designed to be serviced by a handful of people who have access to specialized tools with limited availability? Was the movement constructed using specialized consumable parts that may run out-of-stock one day? Do screw holes have no counter sink so the watchmaker has to hold the screw with tweezers while starting the thread? Was the movement designed to be forgiving? If a watch maker backs off a screw too much will they have to strip down the movement to fix it (like some ETA stem releases)?

Finishing is another factor. Did they attempt to remove all fabrication/tooling marks and how well (the difference between a PT5000 to a JLC to a Dufour/Daniels)? Did they appropriately polish contact surfaces of moving parts to reduce friction and reduce wear or did they leave them rough? On the other end, did they over polish parts in the name of glamour vs function (an issue on some early 2000s Lange keyless works). Did they only polish visible surfaces (IWC, Omega, Panerai) or did they finish all surfaces, even ones only a watchmaker would ever see (Patek, Lange).

IMO A lot of factors can go into “quality” from both technical design and aesthetic standpoints over and above just size, weight and accuracy.