Too-long-didn't-read version: the new UI is meh, the controls changed a lot but seem better, and a lot of features we unfortunately can't use.
Verbose version
The new Blender is trying to cater to new users, since a lot of what we know changed to make it look and behave more like 3DsMax / Maya. Most importantly, the UI was redesigned (again), and a lot of hotkeys were changed.
New hotkeys and controls: annoying, but overall better
I think you can still use the old hotkeys, but by default a number of them have been changed. Takes some getting used to, but overall it seems it should make things easier in the long run.
Some tools are directly in the 3D view now, which makes it a bit more intuitive (they can be toggled off if you don't use them, which is cool).
There are a few nice modifications too, like being able to use more than 20 layers. Some UI elements have been redesigned or moved to better location, which is overall better. But yeah, it can be rather alien at first.
Bad point: the interface
If you ignore the new controls, visually the interface itself is... Really "meh". The text are more blurry (actually because of a shadow effect underneath them), I don't like either the "dark" or "light" skin either, but fortunately you can customize the colors if you don't mind fiddling with the settings. You can end up with something decent if you copy all the settings from the old Blender.
What you CAN'T customize, is the icons. Not an opinion but a fact: the icons are TERRIBLE. They aren't colored, they aren't greyscale either, they are full black-or-white. Which means you can't easily identify them like in 2.7. Not only that, but some of the drawings just don't depict anything meaningful. Used with the default black theme, it makes the interface a whole dark busy mess.
Bad point: compatibility with old files and Plasma itself
Maybe just an effect of being in beta, but I can't open a Blender 2.7 file in 2.8. You can however use the "File→Append" option, but then your whole scene is read-only, with Blender complaining about objects being "linked" when you attempt to edit them. Go figure...
Also, the old renderer was thrown outside the window in favor of both Cycles and the new Eevee. Normally this would be a good thing, but those renderers don't work at all like Plasma's. I don't know how Korman will deal with that, since the material editor is quite different and lightmap baking might have changed too... I think this is going to be a pain to Hoikas
![Confused :?](./images/smilies/icon_e_confused.gif)
Good point: the 3D viewport
It took me 5 minutes to figure out why it felt so different: the viewport doesn't stutter anymore when you're moving in the scene.
And according to Blender's website, it's now capable of displaying much more complex lighting and reflection effects, which unfortunately won't be useful to Plasma. Ah, damn...
Anyway. The new viewport rendering looks sexy, even though it's incompatible with Plasma. I think I'm going to keep using both versions... Although I would be interested in knowing what you people think about it.