I remember the first time I tried irssi, having come from GUI IRC clients like X-Chat and mIRC, and being amazed at all the friendly conveniences it had, like Alt-A to switch to a channel with recent activity, proper unicode support with sensible fallback encoding handling, full support for colour and formatted text, or /upgrade that lets you upgrade your running irssi without disconnecting from the server. And then there was the extra stuff, like the proxy mode and third-party addons like the XMPP client or “trackbar” that draws a line across each channel at the time where you last looked at it.
These days, probably lots of clients have lots of those features, and some probably have all of them… and a GUI client would probably make them more discoverable. But having all those features in a client I can run inside tmux is pretty great, and I expect to be using irssi for years to come.
i use irssi + tmux on a server that is always on, really a simple solution but i never miss any messages.
My big issue with irssi was the way you have to refer to windows by number in order to switch them. Gets really old, really fast.
I prefer a bouncer like ZNC and a graphical client. (IRC is one of the RARE use cases where IMO a GUI helps. A LOT.)
Unfortunately, irssi still can’t split vertically