I would like to preface that I am big supporter of Elastic, I am just providing constructive criticism.
So, I was able to explore a bit with the pre-release. I actually being waiting for v9 after hearing how much improvements will come.
Here are my initial thoughts: I was very underwhelmed 
The UI/UX seems to have made small unnoticeable improvements. The biggest improvement would be the new Solution navigation, although this was released already to cloud. Navigation in Elastic is such a big pain point for many end users and this will help. The only noticeable new change was the UI theme palette. This was needed as it provides a bit of a fresh look. Although I am not sure how I feel about the blue for dark mode, looks like OpenSearch. I also liked how the dashboard layout is now showing a dotted layout which can be used to see where you can scale a visualization.
Things I expected in v9 from UI/UX:
- more intuitive UI
- new visualization types in Lens
- new rules or more intelligent rules (O11y)
- fitting more in a dashboard
- scheduled reports (outside of watcher)
- AutoOps for stateful
- improvements to Graph
I understand that I could monitor the GitHub repo to see what feature requests like above were worked on and merged but I assume a new major version would consider these. Overall, this just feels more like 8.19.0.