My thoughts:
- In case you left before the change, Nemesis brought with it a First Contact rework that was very needed (First Contact now runs off envoys and basically like the archaeology system). This really helps clean up a dated part of the early game.
- The intel and espionage system tends towards the underwhelming. Stellaris has not escaped the 4x espionage trap, where it's either too weak to be satisfying to use or too powerful for being on the receiving end to be fun.
- Meanwhile, the admin cap system has been removed in favor of something much more like the old tech / unity scaling. This means some level of sprawl for an empire is basically inevitable, which helps tamp down some amount of the snowball. With that said, administrators are now just another unity source, which is less good, and some people dislike that empire sprawl is unavoidable. Probably good in the long run, but some friction in the short term.
- More generally, there were some performance improvements that seem to have been lost in the most recent patch, so it's about a wash in total. The AI seems to be more competitive later in the game, but by mid-game a player comfortable with the game can still get a solid lead.
Please don't take this as me denigrating the hard work the devs have put in over the past year, especially when things like the first contact system have revamped outdated systems; it just means the basic game structure hasn't changed, and the consistent challenges the game's development has faced (snowballing, AI, performance) remain to a greater or lesser extent. As for the upcoming expansion, I think it will once again clean up an old and cluttered system, but it won't reinvent the game.