So I downloaded the PDF for Starfinder (have the book pre-ordered from Amazon, but won't see it for a couple of weeks). What a monster.
I'm 9000% a sci-fi guy and I really Paizo's work but man, this stuff is like MAJORLY complex, especially after getting used to 5e. The rules are THICC. The corebook weighs in at 500+ pages. As much as I'd like to play this, I REALLY don't want to GM it and I doubt I'll be able to find someone to take up the monumental task of learning all the ins and outs of vehicle combat, space combat, vast, vast class options and such. I still really want to play it though.
Each player has stamina points that you exhaust before getting to your hit points. You have an energy AC and a kinetic AC. There are tier after tier of weapons, armor, power armor and all the weapon classes and armor types have levels in addition to everything else on top of a massive, massive modding list for them. There's a huge cybernetics ruleset, huge starship ruleset, small vehicle ruleset, combat, skills etc. It's all based on Pathfinder's 3.75 approach. The setting is the future of the Pathfinder Golarion setting, so it's got magic to boot on top of everything else.
Shit is dense.