As far as I understand it (cuz I actually totally missed the DLC's release for a month) much of the negative response and reviews come from initial buggy release, so just like EU4's Leviathan. I bought it few days ago because I just wanted more Surviving Mars and didn't actually notice the negative reviews... and gotta say, it's not good.
I like asteroids, they are pretty and their little gameplay is actually quite nice, but the reason you go there is to get materials for underground, which is a problem because underground is not fun. It's tedious to explore, requires much investment of research into a basically otherwise pointless tree, is micromanagement heavy and just takes a lot of effort to set up... just to give you nothing in return.
In my experience it's something to get excited about, get met with tedious gameplay that just isn't fun, finally get to a point where you can start exploiting the underground, feel it's not worth it... and then just completely ignore it is a thing on next games.
