"Alien Tech" has been removed. All technology options are built traditionally, and now have 7-tiers with names. Red, Green, Grey, blue, Purple, Yellow, and White (aka: Space/Infinite research).
Infinite research are ~7 or so techs at endgame which go on infinitely. +Weapon damage for the most part, but there is also +Productivity (which makes mines last longer and mine faster).
In effect, the core gameplay loop has been extended into an infinite endgame loop. The late game techs are extremely powerful and automate everything that was boring ~5 years ago (ie: killing biters became boring. So its now fully automated with artillery trains).
Forget biters, nuclear bombs quickly remove large numbers of trees, which are the true enemy!
On a more serious note, there have also been countless quality of life improvements, like high-resolution graphics, reworked UI, or copy-and-paste (literally just Ctrl-C / Ctrl-V, I have used it even without robots, its so convenient). If you have radar coverage, the map allows zooming in fully (rendered just like the normal view) and you can place blueprints and issue deletion commands anywhere on the map without moving.
Incidentally, you can also order artillery strikes to play a 'prank' on your unsuspecting friend who is standing motionlessly. (Which is why I made a habit out of standing close to the most expensive thing in the vicinity.)