killersheep VS vim-awesome

We all know that the real must-have plugin is vim/killersheep.

I guess that I sort of did actually answer your question: there are plugins that work on Neovim but not on Vim, but the only plugin I found that worked on Vim but not on Neovim is vim/killersheep, so you get more plugins at no cost.

I'm looking for games (snakes etc) that can be played inside vim/nvim but I haven't find good ones. killersheep can only be played in Vim, vim-snake doesn't work that fine ...

You can play the killer sheep by the grand master. :KillKillKill!

Playing hidden game in vim

I encourage you to add plugins to your vim (tip: use vim-plug). Use vimawesome.com for inspiration.

I don't have a solution for each one of your points, but I'm going to point out a couple that are very useful for me at least (most of these can be found on a site like vimawesome or just native configuration/usage).

Vim Awesome. This is probs the best resource for text editor related plugins for vim. Browse around the site and see what looks like it would work for you. Fugitive, NerdTree, Syntastic, and surround are pretty great for utility.

Get inspired and find your new plugins at https://vimawesome.com/

I originally landed on https://neovimcraft.com because of https://vimawesome.com

then linked to a very useful guide and repository of plugins

Vim is infinitely customizable. While Vscode allows you to change the app’s color scheme, install plugins, and change a few app settings, Vim offers you complete control over the editor’s experience. You have thousands of plugins to choose from. You can completely remap any keybinding and create new shortcuts for tasks in your daily workflow. And giving you more power as a developer, you can completely reprogram or automate your Vim experience with the built-in Vimscript language or Lua for Neovim.