I filled it out yesterday, but more generally:
Diplomatic actions and subject interactions are in a great place. They work, they're intuitive, they're impactful. Adding more options is always welcome, but it's generally great as-is.
I have a few quibbles with power blocs and global rankings (there's space for more depth or rebalancing, but they're not urgent). They work, they're generally fun.
Diplo plays, and to a lesser extent war goals, are the big issues: they're too rigid, and they're not predictable enough. When I am frustrated in the game, 9 times out of 10 it's a result of diplo plays: great powers randomly interfering in conflicts they shouldn't care about, inability to negotiate conflicts, and similar issues.