YMMV / Episode Two Our Mutual Fiend

• Breather Level: The first half takes place inside White Forest, another major Resistance base, and is dedicated mainly to exposition and exploring the base. After repelling a Combine attack on the base, the player is then treated to a second breather which features more exposition, a tutorial for the Magnusson Device, and some character development for Eli and Kleiner.
• That One Achievement: "Neighborhood Watch". This challenge is notoriously difficult because it requires you to complete the Boss Rush at the end of the game without losing any of the major structures. Completing the rush is difficult enough on its own, but with the extra challenge, it's nigh-impossible. To make it worse, some Striders are scripted to blow up one of the buildings immediately after spawning, with the only way to prevent it being at the exact place where they spawn, at the exact time, with a Magnusson Device already ready, which is as much of a Guide Dang It! as it sounds (sometimes it even requires outright ignoring the previous Strider). As of October 2020 it's the second-least-accomplished achievement after "Get Some Grub", with only 6.8% of players having it.
• That One Boss: The massed Striders you face at the end of Episode Two. We've got Hunters everywhere, Magnusson whining at you constantly and the Magnusson devices. Depending on who you talk to, it's very much a polarizing moment.