* The feed is chaotic & no guarantees people (and by extension, Topics) whom you followed will show up primarily. Seeing a machine learning thread between a Barbie post & scantily clad influencer is bizarre.
* The feed is jumpy with tiny accidental refreshes. You could be reading the thread and do a deep dive, and come out to find the timeline slightly/significantly different.
* No message/DM. No bookmark feature. No topic suggestions - Just pure Instagram-like scrolling.
The good part is no ads. But that could be a matter of time. Overtaking Twitter in engagement will be hard. Social networks have some inertia & needs some key users to remain successful (I forget the paper name - but it describes growth/implosion of network graphs when some key community members used/left. Like a hole in the graph. If any HNer knows about it - It came about 7-8 years ago.)