I managed to get into the Horizons Beta over the weekend and after an embarassing episode where I accidentally dropped all my cargo - including the SRV - when looking for the headlight switch of the ship, I even amanaged to play around a little bit on the surface.
It's also clear that the Horizons release will be a very close shave. They have their basic planet generation down, settlements and places to land and take missions are there, there's the mechanic for generated POIs, which is a bit shaky in some corner situations (e.g. despawning when you mve too far away from them with the SRV to access the ship), and the SRV mechanic is implemented. A lot of things can/need to be improved though. Probably even beyond the initial release.
I've started a
list with the glitches/unfinished things and areas for improvement I could find in the official forums. Those are only the most notable issues currently in the visuals, but there are surely more.
Has anybody else found something to add to that list? The rendering of accessible planets on the system map as wireframe instead of a low-LOD presentation is imo also an area where Horizons still needs improvements. Then there is the dust thrown up by the SRV which sometimes doesn't seem to match the surface (e.g. brown dust on white ice surfaces).
And then there's the lack of horizontal displacement, which lets all mountains and rocks in Horizons look like peaks of "molten ice cream", vs. for example the great mountains in Outerra.