

Now for the real question: is it actually IRC or just an in-game IRC-like interface?
The greatest hacking game of all time, Uplink, has an actual IRC client that you can buy and install on your in-game systems.
IRC pops up a lot in less obvious places too. The in-game chat in Warframe is IRC, but it handles all the server and channel connecting, locking you out of connecting to arbitrary servers.
Brotherhood and Revelations are both continuations and upgrades from 2. I would not recommend playing all three back to back, but if you liked 2 they should be high on your list to play next.