I don't really see military FPS games dying out like Guitar Hero. Guitar Hero and Rock Band were niche products for a relatively limited market. Yeah, they were really popular, but that's because they were a fad. Military FPS games aren't a fad, they're a set genre dug in stone by now.
Military FPS games won't be decreasing in popularity anytime soon, even in an oversaturated market.
It'll be fun, for sure, but for how long? That's something every FPS maker asks to make successful games. Activision is literally trying to solve that question by pumping out Call of Duty games every year.
I personally won't mind getting a pirated PC version of this and have fun with the single-player and some LAN with my friends. If you're wondering how I can do that so easily, I live in muthafuckin' China.