Recs.
Updated
SpecsUpdate
Pros
Pro Keyboard-based, mouse-free interface, support trackpad
There's no need to reach for the mouse or the ctrl/alt buttons again. Everything is 1 or 2 key presses away with almost 200 functions specifically for text editing. Vim does support the mouse, but it's designed so you don't have to for more efficient usage.
Versions of vim like gVim or MacVim still allow you to use the mouse and familiar platform shortcuts. That can help ease the learning curve and you'll probably find you won't want to, or need to, use the mouse after a while.
Pro Productivity enhancing modal paradigm
As with all vi-like editors, Vim provides a modal paradigm for text editing and processing that provides a rich syntax and semantic model for composing succinct, powerful commands. While this requires some initial investment in learning how it works in order to take full advantage of its capabilities, it rewards the user well in the long run. This modal interface paradigm also lends itself surprisingly well to many other types of applications that can be controlled by vi-like keybindings, such as browsers, image viewers, media players, network clients (for email and other communication media), and window managers. Even shells (including zsh, tcsh, mksh, and bash, among others) come with vi-like keybinding features that can greatly enhance user comfort and efficiency when the user is familiar with the vi modal editing paradigm.
Pro Asynchronous I/O support
Since Vim 8, Vim can exchange characters with background processes asynchronously. This avoids the problem of the text editor getting stuck when a plugin that had to communicate with a server was running. Now plugins can send and receive data from external scripts without forcing Vim to freeze.
Pro Flexible feature-set
Vim allows users to include many features found in IDEs and competing editors, but does not force them all on the user. This not only helps keep it lighter in weight than a lot of other options, but it also helps ensure that some unused features will not get in the way.
Pro Can never outgrow it
The fact that very few, if any, people claim to be a "Vim Master" is a testament to the breadth and depth of Vim. There is always something new to learn - a new, perhaps more efficient, way to use it. This prevents Vim from ever feeling stale. It's always fresh.
Pro Ubiquity and portability
Vi/vim exists on almost all Unix-like platforms, it is the de-facto Unix editor, and is easily installed on Windows. All you need to make it work is a text-based connection, so it works well for remote machines with slow connections, or when you're too lazy to set up a VNC/Remote Desktop connection.
Cons
Con Doesn't play nice with the system cut/paste mechanisms
This can be worked around somewhat if you disable mouse for insert mode. You can then right-click your terminal and use paste like you would anywhere else in a terminal.
But it still doesn't feel right when the rest of your system uses Ctrl-C/Ctrl-V, and you have a system clipboard manager, and so forth.
Con Poor support for external tooling
Many plugins depend on optional Python and Lua features, which may or may not be included in whatever binaries are available for your system. And without platform-specific hacks, it is difficult for plugins to operate in the background or use external tooling.
Con Poor feature discoverability
Though basic features like syntax checking, autocompletion, and file management are all available out of the box or with minimal configuration, this is not obvious to new users, who might get intimidated or assume they need to install complex plugins just so they can have this functionality. Other features new users might expect to find embedded in Vim, such as debugging, instead follow a UNIX-style model where they are called as external programs, the output of which might then be parsed by Vim so it can display results. Users not familiar with this paradigm will likely fault Vim for lacking those features as well.