My experience with 11.4 on my iPhone X and iPad Pro 9.7 has been quite good thus far. Battery life seems to be slightly improved and everything seems to run a bit smoother.
A few things I've noticed:
Message in iCloud works well but not perfectly. There has been a few times when I've been away from home and deleted a message on my iPhone X and it was still on my iPad Pro when I got home. This has happened a few times when my devices haven't been in close proximity to each other. Not sure if that would effect it or not?
Airplay 2 hasn't been perfect either. With my 2 Apple TV's it's been difficult to get it to play a different song in each room, when using the Home App, sometimes when I pause or play one, it pauses or plays both, at times when both are playing and I use Siri to play something different on one then the other stops playing.
Maybe that's why 11.4.1 beta came so quickly. Hopefully it addresses these issues.