It's an enjoyable enough game, definitely looks nice. However it uses a LOT of resources. I accidentally left my word processor open and had to restart my computer. Also, I loved the GNN reports but had to disable them as they started to freeze the game.
I never had pollution problems, so I don't know if I was just how I was building, or if it's a feature that was never fully implemented. Oddly managing my planets populations didn't feel too micromanagy, but balancing my costs did. I am glad FO does not use money.
Leaders were interesting. However I think I would rather be able to have more, or have their effects be stronger. You don't really get to "choose", so much as decide weather or not you want a particular leader. Also I got a whole lot form neighboring aliens, and a couple of times wound up with most of my leadership being other species. I think once all because all my early ones were really bad. Which honestly mead me feel like immigration probably should have been a thing. Or maybe have it impact, or be impacted by my diplomatic status?
Spies are expensive. The combined research, production of the building, training and pay are a lot. Really the counter intelligence and the prisoner exchange bargaining chip in negotiations might actually be more worth it in the long run than espionage. It does give you a good advantage if you can steal tech or sabotage an empire early on, but later in the game it's kind of pointless.
Diplomacy needs more options. Like seriously, so many problems could have probably been solved if I could have just asked the Darlok to stop poking the bear (in that case bug). Their empires is like 5x yours, just don't. Likewise asking empires you know, for contacts that they know, would have helped move things along, a lot. Diplomatic options are not well balanced, or at least whatever balance they are going for isn't clear. I'm not a complete fan of Stellaris' point-buy diplomacy but more transparency in the diplomacy screen would have helped, as I found a few times where I had great relations with other empires, and all the right prerequisites but couldn't get them to make an alliance and never did figure out why.