I've recently installed OpenSUSE Tumbleweed and when messing around with 'Extension Manager' and
I found these to be the best extensions for Gnome in my opinion.

And the extensions are:

1: Caffeine
Disable the screensaver and auto suspend.

2: Blur My Shell
Adds a blur look to different parts of the GNOME Shell, including the top panel, dash and overview.

3: Dash To Dock
A dock for the Gnome Shell. This extension moves the dash out of the overview transforming it in a dock for an easier launching of applications and a faster switching between windows and desktops.

4: Just Perfection
Tweak Tool to Customize GNOME Shell, Change the Behavior and Disable UI Elements.

5: Shutdown Timer
Shutdown/reboot/suspend the device after a specific time or wake with a rtc alarm.

6: ArcMenu
Application menu for GNOME Shell