Whenever I try to explain Warframe, I tell people its like Phantasy Star Online meets Rainbow Six with wall running.

Each warframe (character) offers their own strengths, weaknesses, and bag of special tricks which you can tailor to whatever playstyle you choose. The ever-expanding list of weapons and warframes paired with the stat-altering mod-system makes customization both easy and rewarding.
Indecisive?
Or just full of ideas?
Not a problem. There's a load-out system that will allow you to save different mod setups as well as different color setups.
While combat is generally fast paced, how you approach it ultimately sets the speed. Run through with guns-a-blazin' or sneak around with a sniper rifle. Riddle the field with a gatling gun or beat people to death with a sci-fi sledge hammer. How you fight through the snow planets, desert planets, warships, vaguely potato-shaped mining facilities, and other levels is completely your call. Or you and your friend's call, because teams can consist of up to 4 players.
Best of all, the game is easily accessable to both the employed and those with slightly moth-infested wallets.

Go kill something.