V8 is really good:

- The file manager UI (Folders, right click. Shift to select more than one file an so on) look like the classic Windows UI (Its really amazing). This is the best feature for me.

- The new text editor is one of the best i ever seen :) Really great. In the future i hope you will add the option to localization (set language) - this will be helpful.
http://ckeditor.com/demo#localization...

- The admim is faster :)

- A lot of small ui design improvements

Cons:
- I dont understand why "legacy form" is so hidden in the UI (under express forms results as button?)
- Add some way in the file manager table to see the "set" (as col in the table - like width or title)

I haven't had much time to play with it, but installed it a few days ago along with a server update that allows me to run it with PHP 7. So far, I quite like it. It seems fairly quick and there is a lot of small improvements and changes. Looks like a lot of work has happened.

The new text editor will be easier for clients to deal with. I've grown to like Redactor, but this makes it easier to find what you're looking for.

File manager changes are great. There are so many sites that I can clean up more easily when this update rolls out officially.

I like the styling on the forms throughout the interface, with the exception of the real estate they take up on modal windows. The old form block was tricky enough and now it's really tedious to scroll forever every time a question is added. Maybe it's just something I need to get used to, but they are a bit harder to read and interact with.

Lastly, a simply guide to getting started with Express Data Objects would be really great to have. I think this unlocks a huge amount of power with Concrete5 but can't be sure as I'm flailing away with anything I try.

I'm looking forward to testing this out further and an eventual launch. I just did some updates to a couple of 5.4 sites and it's exciting to have watched things evolve from that state to where we are now.