What makes Mercenaries 2 awesome is that options are always present -- not just before a mission, not just out in the open world, but at any and all times. And what your best options are is always subjective. There are so many ways for an encounter to turn out. Options and dynamics are a powerful combination.
One common mission in the game is to "Verify" a person, which means to either capture that person or kill him and take a picture of the body. Once, I tried to sneak up and scout a camp with a sniper rifle before entering. But I was spotted! So I immediately rushed in with my assault rifle. If an enemy was close enough, I bashed him with the butt of my rifle.
Someone sounded the alarm, so now all the barracks are alerted and guys are shooting at me through windows with rocket launchers. Someone outside is shooting an RPG as well. I shoot him and rush over to replace my sniper rifle with his RPG (only a couple shots left). I kill some of the men in the barracks, but more show up at the windows. So I throw some C4 on a barracks, run away and hit the detonator. Boom! Now there's rubble of a building to hide behind as I regain a bit of health.
Meanwhile, more enemies are showing up in SUVs with mounted guns. Ouch! Those turrets hurt. Rather than blow them up with my grenades or C4, I strafe and shoot the men on the mounted guns to conserve my explosives. When a man on the turret goes down, the driver gets out, so I immediately rush over to bash him in the head. I exchanged my assault rifle for his LMG (light machine gun) -- shorter range, but tougher.
Someone's called for reinforcements. There was a warning that he was doing so, but I couldn't get to him in time to stop the transmission. Now there's an enemy helicopter shooting at me. I don't have an anti-air missile launcher with me. What I do have is a grappling hook. I duck behind a building and the chopper comes closer to get a better angle on me. Once it's close enough, I rush out from behind the structure, launch my hook, grapple up to the helicopter and pull the driver out. Now I'm flying around the camp. I pick off a couple soldiers with the machine gun, but a series of RPGs bring the chopper crashing to the ground. I survive.
It's time to lay down the hammer! I decided to call in my own support. I have a choice of vehicles, munitions or airstrikes to call in. I call for a tank... one of five tank models available to me, which I purchased with some of my money earlier. It's a light tank, but all I need to finish the job. A helicopter flies in as I shoot the RPG-bearing enemies who try to take it down. The tank drops, I hop in... and everybody dies. :)
I've thinned the resistance, so I make my way to the target. He's holed himself up in a bunker. I run inside and knock him down, then hit the Y button to subdue him (tie his hands behind his back). I still have to carry him to open ground where I can call an ally helicopter to extract him. There are still enemies around shooting at me. And again they call for reinforcements.
I get my man to some flat ground behind the bunker as enemies continue to shoot and call for extraction. A pirate chopper (my allies) land down and I throw the target in. The chopper immediately returns to the air. Normally, I just throw the target inside and fight my way out. This time, I jump in the chopper myself as it's already moving. Guns fire from below. Enemy helicopters patrol nearby. But we escape, and I get paid.
Most battles in Mercenaries 2 aren't this long (more than you'd expect, though). But I wanted to offer a sense of how many options and dynamics are at play at any given moment.
At any point in that battle, I could have called in an airstrike or airdrop -- tanks, helicopters, boats, laser-guided missiles, cluster bombs, anti-chopper or anti-tank fire, RPGs, C4, shotguns, sniper rifles, etc. At any point, I could kill an enemy and tank his weapon or hijack any vehicle. I could hide behind buildings or I could blow them up. I could call for first aid kits or take my chances. I could fight up close or from afar. I could enter in any direction and leave in any direction.
Meanwhile, I was surrounded by variables.
It's not rare for a game to have plenty of options. It is rare for a game to make so many significant options available constantly, including during scripted missions.
The Mercs 2 mission that begins with an oil rig is one of the best missions I've played in any game. Epic, exhilirating and full of freedom.