Well the diplomacy area is unlike anything I've seen in a 4x game. You have casus belli, reputation matters a lot, you can set embargos, warn a faction someone is asking for support against them etc.
The espionage area is pretty awesome as well, you can order your spies to assassinate ministers from another faction, you can get useful information like how many funds they have, and they are doing economically, how many ships and armies they have etc.
The ai is pretty good already, and the devs say it doesn't cheat (personally it does look like they are telling the truth, I never noticed anything and if it did you could discover easily thanks to the espionage module).
Planet management is incredibly well designed as well. If you build too many factories the planet will go into over exploitation and the resources will slowly deplete, you have to be careful with the security and health of the population, etc. The really cool thing is, unlike moo2 where the game forces you to micromanage each colony, in star lords you don't feel the need to. Even if you have 30 planets you don't feel overwhelmed because you don't have to babysit each one, and you can access all the relevant info for each in the planets menu.
The equivalent of leaders is called ministers. They have a certain age and they can die of old age or by assassination (possibly other causes, these two are the only ones I got so far). They are pretty expensive to maintain but they usually bring significant bonuses like better trade, diplomacy, etc.
The game has loads of potential and it's already pretty fun to play. I recommend it, it's really good.