Just played three rounds as the firebug on normal. It's fun if you like KF2 and if you are not a jaded faggot. It's a good horde shooter/coop game.
Things that haven't made that much sense yet are the weapon modifications. They seem rather expensive for what they offer, and you might be overly starved hard on cash buying one each match.
Have they said about adding more modifications on launch? Because two or three per weapon seem quite sparse in options for a feature they have advertised with as being a drawing factor.