-On Expert, this mode is the ultimate L4D challenge. For starters, you're stuck with the typical Realism ruleset. This mean no glows, stronger infected, no mid-level respawns, Witch insta-kills, etc.

-Unlike regular Campaign / Realism, there are no ammo piles through the entire game, meaning you're forced to switch up your weapons instead of relying on that AK / Military Sniper with a laser sight you got way earlier in the campaign. Once you fire that last shot, that's it, better pick up a new gun whether you like it or not.

-Team wipes don't restart the level, but instead send you back to the lobby to start the entire campaign over from the beginning. This adds an extra layer of tension once you finish the first level of any campaign since one mistake is all it'll take to lose everything.

-Griefers are a huge threat in this mode due to the aforementioned return to lobby if your team is wiped. Therefore it's advised you either play this mode with a full team, or set the game to private (not friends only) if you don't want to risk being killed for no reason.

-Common Infected are way more durable than normal due to the mode using Realism as a baseline, making them significantly more annoying than they'd otherwise be.

-Just like Versus modes, new players will ruin your match very quickly, especially if you're playing on Expert. Whether it be constant friendly fire due to their poor aim, getting separated and grabbed only to not communicate where they are, thus dying, or the reverse, you getting grabbed only to not be saved because the newbie is blind and deaf. My suggestion is exactly the same as in Versus; just kick them before they can become a problem.