I just installed Ubuntu 18.04 and one of my first negative impressions is the long animation of flying-in icons when opening the app menu.
Can I speed this up or disable it?
Yes, it is possible.
The link shows you how to turn off all kind of animations especially the spreading icons on menu, searching, and window animations so you can work faster. To do it, just run this command:
$ gsettings set org.gnome.desktop.interface enable-animations false
Then apply it by pressing Alt+F2 and type r and press Enter. This will reset the GNOME Shell to follow your command.
To revert it back (enable animation again), just change the command to:
$ gsettings set org.gnome.desktop.interface enable-animations true
If you're annoyed by only the "Show Applications" animation, you can disable it by running the following in Terminal
gsettings set org.gnome.shell.extensions.dash-to-dock animate-show-apps false
If you want to get rid of all the GNOME shell animations, run the following instead
gsettings set org.gnome.desktop.interface enable-animations false
You can also speed up GNOME shell animations following this: How do I change the speed of the app drawer appearing?