It's like Marathon With Guns.
But to be serious this is a great game and definatly worth a try at least. It plays like a typical classic shooter akin to Doom, Marathon, Duke Nukem, ect. But one big thing seprating it is the Roguelike RPG elements that the game is based on, when starting you can pick a set of starting equipment such as the Soldier which has a fully loaded assault rifle and some decent armor to start or The Prisoner which starts barebones but can take two Perks instead of one at the start.
Once you start it's pretty self expanatory. You have 100 randomly generated floors to go through with momentary safe rooms spaced between each one that allows you to Upgrade/Repair weapons and buy ammo and health for the next set of floors. You can find a number of weapons off of Enemies that you fight which can drop on anyfloor off of any enemy ranging from a Realtivly weak Katana to a ♥♥♥♥♥♥♥ Rocket Launcher. The levels are pretty easy but get harder and harder the father you get up, Of course this can be said of any game but as anyone who plays Rougelikes knows: Once you die, you lose everything and have to start again.
There is plenty of replay value to be found in this game, the more Intel you collect throughout the game you gain bonuses such as Health and Damage upgrades that can carry over to the next game and Higher Diffulcuty levels if your man enough for them.
To put it simply: this is a great game overall and well worth the 10 bucks you can get it for ($4 as I write this during the summer sale).