My CC 2018 installation experience.
FWIW - my initial experience... On Windows 10 desktop, broadband connection (50+mbps)
First, the Creative Cloud app had to update itself. Always the case. About 5+ minutes.
Then, update Photoshop only. Big download, somewhere between 10-15 minutes. BEWARE, you have to click the "advanced" option to keep it from wiping out your old version.
Installation completed, no errors, yet still no desktop icon created. You still have to navigate the Start menu, or find the exe and create your own desktop shortcut icon. My old version (2015.5) was still fully finctional after 2018 install.
However, 2018 loads the new Camera Raw.8bi and wipes out whatever old version you had. So your old version of Photoshop and Bridge now have the new camera raw. And as with all prior updates, a new camera raw causes Bridge to re-generate all its thumbnails.
So, as you navigate folders with Bridge, be prepared to wait for thumbnail generation. On my system, it takes about 2 minutes for a folder of 300 images, while Bridge uses 35% to 40% of the CPU. This is an unnecessary and unfortunate side effect that I and others have complained about for years on Adobe forums.
I have 6 Topaz plugins, the NIK collection, and 3 other plugins. I told the install to copy all, but strangely, only Topaz Denoise showed up. However, a simple drag-and-drop of all plugins from the old Photoshop to the new plugins folder worked. All plugins now appear in 2018 and work OK. My custom workspace was copied in tact (panel positions, colors, etc.)
First thing I wanted to try was the "Curvature" Pen tool, but it was missing in the tool pallet. A quick Google of "Curvature missing" reminded me that I had customized my tool pallet and new tools have to be added.
The new 2018 Photoshop uses slightly less memory, and is faster to virgin launch. My CC 2015.5 is 902mb after launch, before opening an image. My CC 2018 is only 730mb.