1. After the mandatory mark and execute, run full speed at the next merc by the fence and use Sam's sliding move that he does when he goes from a run to a crouch to slide tackle the guy. Then shoot him while he's down.
2. If you take the window route into the warehouse, climb the pipe and position yourself above where the guard patrols underneath it. Mark the two guards standing together by the pit and the guard across the room by the door to the hallway, throw a sticky camera into the little office with the guard on the computer, and aim your crosshairs at the EMP thing hanging from the ceiling. Wait until all the marks are red and the guy underneath you is in the right spot for a 'death from above'. Then detonate the sticky cam, tap the right trigger twice to shoot down the EMP thing, hit execute to take out the three that are marked, and drop on the last sucker.
(Six guards down before they even know you're there = feeling like a true bad@$$)
3. After going down into the sewer, the first three guys talking about you can be taken down without a mark and execute. Just stand up in the dark corner next to the guy giving the lecture. Two quick headshots to the idiots standing next to each other and an immediate hand-to-hand takedown of the surprised guy right next to you is proof enough that whenever you can avoid using the mark and execute and still pull off a sweet move it's definitely worth it.
Not so cool:
1. If you grab one of the guys out front and throw them (how Sam has the superhuman strength to do this so well, I have no idea) up on the truck expecting their head to very satisfyingly break the windshield, they will instead disappear through the hood. (Serious clipping issue)
2. The annoying bug where a merc falls but the sound effect for when they hit the ground repeats about twenty times and makes that annoying clicking sound.