If a picture is worth a thousand words, then surely the above screenshot could replace the quite lengthy title of the game. Flames? Check. A mercenary? Yup. So there it is, Mercenaries 2: World in Flames. IGN has posted a hands on preview of the game as played in co-op. Perennial favorites like seamless drop in-drop out co-op make the feature list, and there are a few other nice little touches as well.
Money and weapons earned while playing in the host's game will transfer to your own game, though progress through the content will not. The game's difficulty will not scale with the addition of a buddy; this is likely not too much of a problem due to the sheer number of enemies and toughness of many of the game's areas. In co-op, players can resurrect each other, rather than failing the mission and having to restart, which is a tremendous benefit.
The preview gives details about a couple of the missions from game, which sound quite entertaining. This quote pretty much sums it up:
It's really quite something to watch a building vaporized and see a mushroom cloud bloom from its ashes.