I didn't have a lot of time with the first Mercs, my cousin brought it over, and it's best described as a cross between Star Wars Battlefront, Grand Theft Auto, and the most load-tastic game you can think of. that might have been just my crappy PS2, but still. Mercs 2 takes away the the crippling loads, adds in some much prettier graphics, online co-op and... that's about it. that doesn't make it a bad game, i wouldn't say that at all, but if you have the original Mercs, i suggest saving your money and holding out for the upcoming holiday rush. especially if you're considering the PS2 version. i've seen videos and it's terrible. THE worst pop-in i have ever seen, and crappy excuses for explosions, but i'm here to talk about the current-gen version...
speaking of the original mercs, its subtitle sums up both game's concepts: "playground of destruction" i didn't get a huge thrill out of doing story missions, but i never got tired of blowing stuff up. be it with tanks, C4, RPGs, take your pick! the destructible environments aren't entirely realistic, but they look good, and they don't get in the way too much. of course, you're blowing stuff up for a reason. the game begins with accepting the mission of an incredibly rich Venezualan to rescue a general friend of his. upon your return they give you a reward: a betrayal, and a bullet up the ass (that might just be with Mattias' story) after that, he takes over Venezuela, and everyone wants to hire you to help them get a piece of the oil! actually the most notable change from the original is that you now have to collect fuel to order things like airstrikes and supply delivery.
different factions will hire you and i did like its system for how factions react to you attacking them. a soldier will start making a call, and a timer shows up for how much time you have to stop them. staying on their good side lets you use their shops and get help from their soldiers. its harder than it sounds since factions are fighting each other, and aren't afraid to make you betray them. you can disguise yourself as a faction with certain vehicles, which still feels off for a number of reasons. they'll get suspicious if you just act normally and shooting at that factions enemies drops your disguise. it just needs more depth.
The three characters you choose don't have many differences. however, they each have one enhanced stat (one heals fast, one runs fast, one gets more ammo) and there are some dialogue changes, so its enough to make you wanna try the game again with someone else. too bad Mattias (mohawked swede) is the only recognizable character. aside from him you have the black guy and the chick.
There really isn't much else to say about gameplay, though the ending mission's a tad disappointing since its just one big quick-time event. its a third-person shooter that lets you take vehicles and blow just about everything up. so if you like explosions, freedom, explosions, driving tanks, explosions, online co-op and explosions, this games for you!

fun fact: this game has the best commercial song in the history of mankind. (youtube it) WHY IS IT NOT IN THE GAME?!