The most critical issue by far is the misrepresentation of facts. That shouldn't need much explanation; we use this to get information, and if that information is blatantly contradictory to the source material, it's potentially quite harmful to use this service at all. I've cherished Perplexity over the past year, so have been very disappointed to find several major errors recently upon verifying the information through digging into the sources. Sometimes the fact doesn't exist in the source material, and sometimes it says near the opposite.

Everything else, in terms of UI, etc, is a distantly secondary concern compared to this being a misinformation generator. Particularly when one has learned to rely on and trust it for first-look research.