OK don't expect anything good i should be asleep right now.
High Frontier 4 All is fairly complex, yet not as complicated as everything thinks. It's simulation type of game so don't expect shitty euro mechanics implemented into space theme. Best thing which is related to the fact that it is a simulation game it's that all game mechanics are scientific. Delta-v, hokmass (or whatever they were called), magnetic fields, atmospheres, hydration on astral bodies etc. etc. Reading rule book itself was honestly an amazing experience.
When it comes to gameplay, HF4 have lots of different mechanics and things to remember (how to land on different sites, how to factory lunch, the requirement to have an engine that will allow you to escape the gravity of the planet) but its nothing uber complex, all most of the information are on the map (which is absolutely gorgeous)
Game is divided into several sequences/stages but they are not set in stone, game just progress in this way.
Since our lord and savior eklund is libertarian, "first phase" is Free Market phase where you auction patents of your future rockets, collect money(which is water and besides being used as money they it's also one of possible fuels for your rocket) and possibly make deals with other players on your future plans (call dibs on possible landing sites) or exchange your passive bonuses.
After you get pieces you deisre you send them to LEO (lowest earth orbit), then make a rocket out of them. and conquer space...
It goes like this >claim size>build factory/possible colony too>and then build better rocket parts (each rocket part is 2 sided- white part is way weaker and can only be created on earth. Black one is x times better, have more effect and can only be created in factory of the which suits her Spectral Type (basically if card is Type A- you can only build its better side on body in space that is also type A)