I believe that without using music theory and music production terminology, the whole "what is goth music" discussion goes nowhere. For me, 'goth music' is characterized by the following:

• repeated rhythms, often in simple time
• use of effects such as chorus, distortion, delay etc on electric guitars (and occasionally bass guitars) to create 'ambient' textures
• high use of reverb on all instruments
• less overdrive/distortion compared to industrial, punk and metal, more subdued electric guitar timbre
• use of noise and extraneous sounds alongside "musical" pitch (especially goth rock that leans more towards post-punk)
• use of synthesizers/keyboards to colour textures with ambience
• use of power chords (as in all rock genres)
• use of minor keys
• less emphasis on instrumental technical prowess and more on creating affect through texture and ambience
• clean vocals, often in a low tessitura

These are core attributes and by all means not exhaustive. All of these attributes create the "dark sound" that goth rock is known for. 'Ambience' is a very important word here when it comes to describing the sound of goth rock that I believe a lot of people tend to overlook. The 'ambient' and 'textual' characteristic of goth rock is shared by shoegaze and dream pop, with shoegaze emphasizing more use of distortion and less reverb and dream pop emphasizing more chorus and reverb and less distortion. The de-emphasis on showcasing instrumental technical prowess is an attribute shared with shoegaze, dream pop, EBM, industrial punk, post punk and post-rock but not with metal and progressive rock.