I used to play Iron Grip with my little brother quite a bit around 8 years ago. Was a great time waster (turning on the xmas option made us both laugh til our stomachs hurt).
First off this game is very not serious. To make it plain as day, this game is almost like a cross between Quake 2 and TFC (engineer class only). You earn money from shooshting (yes it's totally a word... Austin Powers 3 damnit!) bad guys who are trying to invade your... country? You use that money to magically make yourself more and more like rambo... or instead building bunker style turrets that shoosht the badguys, kinda.
Pretty much most of the game you run around using rather stiff guns to blow appart baddies, most of which run the gambit almost like a weird tower defence. Your towers you can build are pretty 'bleh' as they are easy to destroy and have terribly firing arcs. Depending on the map you will have random objectives that will annoyingly take you away from defending the base, and in most cases will cause you to die, alot.
But, once you load the game up with a few friends it suddenly becomes a riot. So if you plan to grab this game on a whim, grab a few more copies and share it with some friends.
Otherwise the toy soldiers win. And nobody likes that.