It’s great to see your enthousiasm! I do agree it is difficult to objectively provide feedback on non-technical issues such as the sound of the plugin. However, this kind of feedback is very welcome, because it can help us determine whether the plugin deserves a spot in the official repository at some point.
A category that the community can provide valuable information on is the useability of the plugin. For example: if a filter plugin has a parameter that allows setting the resonance ridiculously high, this will most likely cause a massive spike in volume. From a useability perspective this may be quite bothersome. Feedback for this hypothetical plugin could be something like “The ability to set the resonance so high gives a very unique sound, but it could use some kind of auto-attenuation on the output level for high resonance values due to volume spikes”.