I'm playing through on Hard currently. The Grunts are pretty much not an issue at all by themselves or even in a group, so the first 20 minutes or so of the game was a breeze. Big difference once they started introducing Snipers. From that point on, I've had to go in with a plan or just get systematically taken apart.
It's not inherently tactical, but the spread out spawn points and the AI of certain things will force me to be more careful than if I was playing a pure TPS like say Gears of War.
Also, I love how huge just some of the stages are both in width, depth, AND height. You can really use the layout of the land to your advantage. Apparently there's a way to get the grenades to act as Proximity mines according to the in game profile on them, but I haven't figured it out. When I do, that will be absolutely enormous fun forcing the aforementioned "Helicopters" to chase me by a prepared outcropping just a little tooooooo close...