Watched some Guerilla mode vids, and it looks kind of lame really. You have one stealth round for every 10 rounds where you basically secure a new "base" to defend. Then the next 9 rounds have you defending it against an ever-increasing number of enemies who will come from all sides. You have a little time to re-arm after each wave, but there's no Gunsmith available in that mode to customize your weapons, so you're just stuck with what you get from the re-arm crates. That was a dumb decision IMO.
It seems to just get very hectic very quickly and you're just trying to cover all sides at once as they try to come in all the various entrances. Not a lot of fun really. I'd rather see a pure stealth mode where I can try to take out a whole area without setting off an alarm. Maybe it's fun co-op, but I don't play multi much, and there isn't any matchmaking anyway apparently.
"The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts." -- Bertrand Russell (I think...)