Highly underestimated and fun, if short.
For a game that wasn't given much critical attention or hype, it's quite fun to play, and has a surprisingly large amount of ways to fight the enemy in every level.
Stealth and sneak kills, setting up traps with mines and/or a sentry gun, running in with guns blazing, going from cover to cover and using suppressive fire, using grenades to flush enemies out of cover or to clear bunkers, sniping from afar, or just flat out smacking people in the head really hard are all very viable options, and you can have Rogue (the main character you play) fight the way you want him to, and most of the time there aren't any wrong choices.
It's this wide variety of ways to play that makes Rogue Trooper such a thrill to play. You never get tired of the gameplay because there's just so many ways to fight. If you feel like sniping, you can snipe. If you feeling like run and gun, you can do that too. If you wanna play the stealthy Rambo type who sneaks around knifing people in the back, that's doable as well (and you get a salvage bonus for doing it; more on that later) and this smorgasbord of options goes a long way in keeping you entertained.
Also, adding an extra layer of depth and some "roleplaying" elements so to speak (stat-building really, which isn't really roleplaying, but I digress) is "Salvage" in this game, basically bits and pieces of scrap and equipment components you can pick of from scrap heaps and from fallen enemies that you can use to build things like ammo and health packs and grenades, and even upgrades to make new equipment or make your existing equipment more powerful.
It's a very fun system and adds an extra layer of depth to the regular run and gun, as depending on which upgrades you build and when, you can get better at a particular kind of playstyle. You can upgrade your sniping and trap-laying abilities for example to be a finesse sort of guerilla warrior, or just up the power of your grenades and the size of your bullet magazines and the power of each bullet so you can run and gun better, or any number of things in between.
The storyline of this game is surprisingly good, if somewhat underdeveloped, and actually follows the main points of the comic book series of the same name that it's based on. I wish it'd been fleshed out a little more, but what's there was still interesting, but actually caused me to buy the Trade Paperback version of the first 2 volumes of comics on Amazon so I could learn more about the background.
The only complaint I have is that the game is a bit short, and although you have a lot of fun palying it, you can finish it in a day or two of involved play, and then all you have left to do is to play the multiplayer game, or browse through the encyclopedia of information about Nu-Earth (the game's setting) and the characters, equipment, and enemies and such. Also, although I found the difficulty to be "just right", some might find it too easy, especially on the "Normal" setting. As this game was made for consoles, the mouse and keyboard setup on PC's just makes you into a titan among cockroaches if you know how to play FPS's well. That said, if you up the difficulty, this isn't as much of a problem, and the last few levels are still quite challenging All in all, I'd say that Rogue Trooper is a worthy buy (it's available on Steam for an online download if that's your thing) and quite fun for the price, although I wish it had been made a bit longer (the last level sneaks up on you, and it actually feels more like the second or third to last level in other games) or that an expansion pack or sequel had been released.