The Facility mission early in the game was a lot of fun. Get all the way to the end where you need to blow the tanks, but don't. Run back through the control rooms and plant the mines in the room with the staircase.
Since the alarm has sounded, an endless amount of soldiers come down those stairs for you to slaughter. You also have one door for them to enter through to get you, so you can bottleneck them. You also have a big window to see the carnage when you detonate the remote mines. They sometimes get blown against the window.
You can kill hundreds of those nameless commies.