Warframe is a game set in our solar system, more or less, far far in the future. How far I have no idea.
You play as one of the Tenno, a human-like race and the only ones capable of operating the Warframes. Warframes are (I think) bio-mechanical armor suits with varying abilities and appearances. Each one does something different, and each one specializes in a particular goal. All of the Warframes will get the job done, just a matter of how you want it done.
For example my current favorite Warframe is Rhino, a hulking mass of armor and unstoppable muscle, with extra armor abilities and a desire to smash things. Literally. He can charge and send enemies flying (if they don't die on impact), or his "ultimate" ability is a stomp "Strong enough to bend time, slowing enemies around him".
I recently acquired Ivara, a sleek female Warframe that really wants nothing more than to hit you in the head, with an arrow, from 500m away, and you not even realize it happened. She's a stealth Warframe with a skillset unlike any other, her primary ability has 4 different modes. The 2 I have unlocked is a small cloaking zone, and a zip-line maker. =D OH and she can manually guide an arrow directly to her target.
There are a lot more than just those two. Here's the official page for all of them.
There are a ton of weapons too. How about a flak cannon that gets more accurate the longer you hold the trigger? Or a modified mining laser than melts people when the 2 beams converge? On top of the standard pistols, rifles, and sawblade launchers.
The enemies leave a little to be desired. They vary in appearance and stats based on faction. Like one has no shields, but a good amount of armor and hp. Another likes to bring robots with them, to boost shields or attack depending on model.
But they all share a generic approach to combat: Shoot the thing or smack the thing. Most enemies can be approached in the same way, the "difficult" ones being the heavies or the specialized attack units. The rest are just cannon fodder really.
In a way that's a good thing. You're an ancient being in a bio-suit called a Warframe. You're supposed to kick ass and mow down those too slow to get away. On the other hand, it makes for fairly repetitive game play and a slight lack in challenge. The hardest parts are when they throw too many enemies at you, not stronger ones.
Recommended if: You like having options, and don't mind smashing the same dudes over and over to reach your goals.
Reconsider if: You're bored by repetition, and dislike a lack of story, because there's very little in Warframe.