Something happened in my current Stellaris game that made me want to share this...
In past 4x games such as Civilization, Endless Legends, Galactic Civilizatoins and Sins of a Solar Empire, I've never had a reason to use diplomacy on AI players. In those games, diplomacy was completely useless as the AI just rejectes every advance I made OR I don't really gain any useful advantage from successful diplomacy.
Not so in Stellaris. The hover tooltips in the diplomacy screen are a godsend. They tell you exactly why the diplomatic move you're making would or would not work and the reasons why. This makes it miles better than the other games where diplomacy relied almost completely on guesswork and luck.
I had been trying to get a friendly species to have a mutual research exchange pact. The tooltips allowed me to figure out what diplomatic moves I had to make to achieve what I wanted. And it was complicated series of moves which I would never have figured out without the tooltips.
The tooltip immediately told this species would only accept research pacts from an ally (does this mean there are species that don't require an alliance for research pacts?). So I tried to ally with them, which tells me you're -16 points shy. Alright, I need to be friendlier to them. I tried a non-aggression pact but again the hover tips said we didn't share a border. I plopped down a colony right next to their border and that allowed me to sign a non-aggression pact and a guarantee independence pact.
Now I'm -6 points shy of being alliance material. but I was also out of diplomatic moves. A couple of months later, another species declared rivalry against this AI species I had been trying to woo. I immediately declared rivalry against that species, and after a few insults they rivaled me too. Ahh nothing like a shared enemy to bring disparate species together. They were finally willing to be allies and I had my research treaty!
I had a really satisfying time planning and executing this series of diplomatic moves.